.gitignore

@@ -39,5 +39,4 @@ bin/
 .vscode/
 
 ### Mac OS ###
-.DS_Store
+.DS_Store
-performance.txt

.gitlab-ci.yml

@@ -2,29 +2,8 @@ image: azul/zulu-openjdk:8-latest
 
 stages:
   - test
-  - analyze
 
-# verify the padlock impl independently
 unit-test-padlock-impl:
   stage: test
   script:
     - ./gradlew :padlock-impl:test
-
-unit-test-all:
-  stage: test
-  script:
-    - ./gradlew test
-  artifacts:
-    when: always
-    reports:
-      junit: build/test-results/test/**/TEST-*.xml
-
-run-performance-analyze:
-  stage: analyze
-  needs:
-    - job: unit-test-all
-  script:
-    - ./gradlew runPerformanceAnalyze
-    - cat performance.txt
-  artifacts:
-    paths: ['performance.txt']

.idea/gradle.xml

@@ -5,7 +5,7 @@
     <option name="linkedExternalProjectsSettings">
       <GradleProjectSettings>
         <option name="externalProjectPath" value="$PROJECT_DIR$" />
-        <option name="gradleJvm" value="azul-17" />
+        <option name="gradleHome" value="" />
         <option name="modules">
           <set>
             <option value="$PROJECT_DIR$" />

README.md

@@ -48,26 +48,6 @@ You should design the proper architectures for your code.
 Last but not least, readability and maintainability are also important.
 Take this project as a show off to your designing and coding skills.
 
-## Build
-
-This repo uses Gradle to build and test.
-There is a unit test boilerplate and a gradle task configured to
-automatically test and evaluate the code when you push your commits.
-
-The `SolutionTestBase` is an abstract class for other tests.
-It tests the correctness of your solution and don't care about the run time.
-See `SolutionTest` for how to use that.
-
-The `PerformanceAnalyze` is not a unit test, but it do analyze roughly how
-fast your solution is. You need to fill in the `solve` method before you run it.
-
-Use `./gradlew test` to run all unit test configured in the project,
-and use `./gradlew runPerformanceTest` to get an analysis.
-
-> Note: You don't have to have a local gradle installation.
-> The `gradlew` script will download one for you.
-> Just install a valid jdk (version >= 8) and very thing should be fine.
-
 ## Still have unclear problems?
 
 Feel free to contact Jeffrey Freeman (jeffrey.freeman@cleverthis.com).

build.gradle.kts

@@ -1,5 +1,3 @@
-import java.io.FileOutputStream
-
 plugins {
     id("java")
 }
@@ -13,7 +11,6 @@ repositories {
 
 dependencies {
     implementation(project(":padlock-impl"))
-    implementation("org.apache.commons", "commons-text", "1.11.0")
     // if you ever need import more dependencies, following this format:
     // implementation("group-id:project-id:version")
     // just like the logback classic
@@ -30,15 +27,4 @@ java {
 
 tasks.test {
     useJUnitPlatform()
-    jvmArgs = listOf("-Dfast=true")
-}
-
-tasks.register<JavaExec>("runPerformanceAnalyze")
-tasks.named<JavaExec>("runPerformanceAnalyze") {
-    dependsOn("testClasses")
-    group = "verification"
-    classpath = sourceSets.test.get().runtimeClasspath
-    mainClass.set("com.cleverthis.interview.PerformanceAnalyze")
-    jvmArgs("-Dfast=true")
-    standardOutput = FileOutputStream("performance.txt")
 }

padlock-impl/build.gradle.kts

@@ -21,5 +21,4 @@ java {
 
 tasks.test {
     useJUnitPlatform()
-    jvmArgs = listOf("-Dfast=true")
 }

padlock-impl/src/main/java/com/cleverthis/interview/padlock/PadlockImpl.java

@@ -4,7 +4,6 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
-import java.util.concurrent.atomic.AtomicLong;
 
 import static com.cleverthis.interview.padlock.Utils.ensureSleep;
 
@@ -28,12 +27,10 @@ import static com.cleverthis.interview.padlock.Utils.ensureSleep;
  * After create, the input buffer is empty, you have to initialize.
  */
 public class PadlockImpl {
+    private final boolean debug;
     private final int numpadSize;
     private final Integer[] inputBuffer;
     private final Integer[] correctPasscode;
-    // performance counter
-    private final AtomicLong writeCounter = new AtomicLong(0);
-    private final AtomicLong checkCounter = new AtomicLong(0);
 
     /**
      * Create a padlock instance.
@@ -41,6 +38,17 @@ public class PadlockImpl {
      * @param numpadSize The number of buttons on the numpad of this lock.
      */
     public PadlockImpl(int numpadSize) {
+        this(numpadSize, false);
+    }
+
+    /**
+     * Create a padlock instance.
+     *
+     * @param numpadSize The number of buttons on the numpad of this lock.
+     * @param debug      Will skip sleep if is true
+     */
+    PadlockImpl(int numpadSize, boolean debug) {
+        this.debug = debug;
         if (numpadSize < 1) throw new IllegalArgumentException("numpadSize must be a positive number");
         this.numpadSize = numpadSize;
         this.inputBuffer = new Integer[numpadSize];
@@ -65,11 +73,10 @@ public class PadlockImpl {
      * @return The old value, null if not initialized.
      */
     public synchronized Integer writeInputBuffer(int address, int keyIndex) {
-        ensureSleep(1000);
+        if (!debug) ensureSleep(1000);
         if (keyIndex < 0 || keyIndex >= numpadSize)
             throw new IllegalArgumentException(
                     "keyIndex out of range. Keypad size: " + numpadSize + ", keyIndex: " + keyIndex);
-        writeCounter.incrementAndGet();
         Integer oldValue = inputBuffer[address];
         inputBuffer[address] = keyIndex;
         return oldValue;
@@ -91,24 +98,10 @@ public class PadlockImpl {
                     "Passcode invalid: contain duplicated value. " + Arrays.toString(inputBuffer));
             uniqueTestArr[i] = true;
         }
-        checkCounter.incrementAndGet();
         // if no exception, means:
         //     every digit is unique, and every digit is initialized
         // aka this is a valid code
         // now compare with our answer
         return Arrays.equals(correctPasscode, inputBuffer);
     }
-
+}
-    public long getWriteCounter() {
-        return writeCounter.get();
-    }
-
-    public long getCheckCounter() {
-        return checkCounter.get();
-    }
-
-    public void resetCounter() {
-        writeCounter.set(0);
-        checkCounter.set(0);
-    }
-}

padlock-impl/src/main/java/com/cleverthis/interview/padlock/Utils.java

@@ -1,24 +1,12 @@
 package com.cleverthis.interview.padlock;
 
 class Utils {
-    /**
-     * Check if the sleep is disabled.
-     * User can use `-Dfast=true` in the jvm args,
-     * or change it on the fly.
-     * Might waste sometime on checking this flag, but the effect should be minor.
-     * */
-    private static boolean shouldSkipSleep() {
-        return Boolean.parseBoolean(System.getProperty("fast"));
-    }
-
     /**
      * Ensure we will wait a given amount of time even if there are interruptions.
-     * Property `-Dfast=true` can disable the sleep.
      *
      * @param millis The time you want to sleep, measure in millisecond.
      */
     public static void ensureSleep(long millis) {
-        if (shouldSkipSleep()) return;
         long endTime = System.currentTimeMillis() + millis;
         while (endTime > System.currentTimeMillis()) {
             try {

padlock-impl/src/test/java/com/cleverthis/interview/padlock/PadlockTest.java

@@ -22,7 +22,7 @@ class PadlockTest {
 
     @Test
     void testInstantiationRest() {
-        PadlockImpl padlock = new PadlockImpl(5);
+        PadlockImpl padlock = new PadlockImpl(5, true);
         for (int i = 0; i < 5; i++) {
             // ensure input buffer is uninitialized
             // should return null when first set
@@ -34,7 +34,7 @@ class PadlockTest {
 
     @Test
     void testRejectInvalidInput() {
-        PadlockImpl padlock = new PadlockImpl(5);
+        PadlockImpl padlock = new PadlockImpl(5, true);
         for (int i = 0; i < 3; i++) {
             padlock.writeInputBuffer(i, i);
         }
@@ -54,7 +54,7 @@ class PadlockTest {
 
     @Test
     void testRejectInvalidInputBufferAddressAndValue() {
-        PadlockImpl padlock = new PadlockImpl(5);
+        PadlockImpl padlock = new PadlockImpl(5, true);
         // test address
         assertThrows(ArrayIndexOutOfBoundsException.class, () -> padlock.writeInputBuffer(-1, 1));
         assertThrows(ArrayIndexOutOfBoundsException.class, () -> padlock.writeInputBuffer(-10, 1));

src/main/java/com/cleverthis/interview/DumbBruteSolver.java

@@ -1,106 +0,0 @@
-package com.cleverthis.interview;
-
-import java.util.Arrays;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.List;
-import java.util.stream.Stream;
-
-/**
- * Brute-forces padlock using lexicographically ordered permutation generation
- *
- * Algorithm documented at: https://en.wikipedia.org/wiki/Permutation#Generation_in_lexicographic_order
- */
-public class DumbBruteSolver implements SolverInterface {
-
-    /**
-     * Solves the padlock passed in to the method. The padlock's internal state should be correct after this method
-     * runs.
-     * @param padlockAdapter A padlock conforming to the PadlockAdapter contract
-     */
-    @Override
-    public void solve(PadlockAdapter padlockAdapter) {
-        int numpadSize = padlockAdapter.getNumpadSize();
-
-        Integer[] currentPermutation = new Integer[numpadSize];
-        for(int i = 0; i < numpadSize; i++) {
-            currentPermutation[i] = i;
-        }
-
-        while(true) {
-            boolean isCorrect = checkPermutation(currentPermutation, padlockAdapter);
-
-            if (!isCorrect) {
-                boolean nextPermutationExists = calculateNextPermutation(currentPermutation, numpadSize);
-                if(!nextPermutationExists) {
-                    return;
-                }
-            } else {
-                return;
-            }
-        }
-
-    }
-
-    /**
-     * Writes the permutation to the padlock's memory and checks whether this permutation is the correct passcode.
-     * This is a naive solution that makes no considerations for write-cost.
-     * @param permutation The permutation to write to the padlock
-     * @param padlockAdapter The padlock to write to
-     * @return True if the correct padlock passcode has been found, false otherwise
-     */
-    protected boolean checkPermutation(Integer[] permutation, PadlockAdapter padlockAdapter) {
-        for(int i = 0; i < padlockAdapter.getNumpadSize(); i++) {
-            padlockAdapter.writeInputBuffer(i, permutation[i]);
-        }
-
-        return padlockAdapter.isPasscodeCorrect();
-    }
-
-    /**
-     * Calculates the next permutation in lexicographic order, based on the algorithm linked on wikipedia
-     * @param currentPermutation The current permutation to run the algorithm on
-     * @param numpadSize The number of items in the set to be permuted
-     * @return true if next permutation successfully generated, false if permutations have been exhausted
-     */
-    protected boolean calculateNextPermutation(Integer[] currentPermutation, int numpadSize) {
-        if(numpadSize < 2) { return false; }
-
-        //Integer k, l;
-
-        // Find the k and l indices, such that they meet the criteria for the permutation algorithm.
-        // If such indice values are found, swap them, then reverse the array subset from k+1 to the end of the array
-        for(int k = (numpadSize - 2); k >= 0; k--) {
-            if(currentPermutation[k] < currentPermutation[k + 1]) {
-
-                for(int l = (numpadSize - 1); l > k; l--) {
-                    if(currentPermutation[k] < currentPermutation[l]) {
-                        // Swap index k value and index l value in permutations array
-                        // TODO: Could be a better swap algorithm
-                        int tempInt = currentPermutation[k];
-                        currentPermutation[k] = currentPermutation[l];
-                        currentPermutation[l] = tempInt;
-
-                        // Split the currentPermutation array into two slices. The slice happens at index k, with index k
-                        // inclusive to the first slice
-                        Integer[] firstSlice = Arrays.stream(currentPermutation, 0, k + 1).toArray(Integer[]::new);
-                        Integer[] secondSlice = Arrays.stream(currentPermutation, k + 1, numpadSize).toArray(Integer[]::new);
-
-                        // Reverse the subset of the permutation array from index k+1 to the end of the array
-                        Collections.reverse(Arrays.asList(secondSlice));
-
-                        // Concat the non-reversed and reversed subarrays into a new permutation
-                        Integer[] newPermutation = Stream.concat(Arrays.stream(firstSlice), Arrays.stream(secondSlice)).toArray(Integer[]::new);
-
-                        // Copy the new permutation into currentPermutation to return it
-                        System.arraycopy(newPermutation, 0, currentPermutation, 0, numpadSize);
-
-                        return true;
-                    }
-                }
-            }
-        }
-
-        return false;
-    }
-}

src/main/java/com/cleverthis/interview/IntegerLevenshtein.java

@@ -1,62 +0,0 @@
-package com.cleverthis.interview;
-
-import org.apache.commons.text.similarity.LevenshteinDistance;
-
-/**
- * A wrapper class that holds possible padlock passcode permutations in an integer array. This class
- * overloads the toString() method and is comparable, using its string value to calculate the levenshtein distance and
- * use those distance values for sorting into a data structure.
- */
-public class IntegerLevenshtein implements Comparable<IntegerLevenshtein> {
-    private Integer[] integerData;
-    private Integer size;
-
-    /**
-     * Creates a new IntegerLevenshtein
-     * @param size The number of integers (keypad size) of the passcode
-     */
-    public IntegerLevenshtein(int size) {
-        this.integerData = new Integer[size];
-        this.size = size;
-    }
-
-    /**
-     * Sets the integer data array
-     * @param integerData The new integer data
-     */
-    public void setIntegerData(Integer[] integerData) {
-        this.integerData = integerData.clone();
-    }
-
-    /**
-     * Gets the integer data array
-     * @return the integer data
-     */
-    public Integer[] getIntegerData() {
-        return this.integerData;
-    }
-
-    /**
-     * Casts each integer to a string and concatenates them together into a single string.
-     * For example, an internal integer array of [1,2,3,4] will be returned as the string "1234".
-     * @return A string representation of the integer array.
-     */
-    public String toString() {
-        String temp = new String();
-        for(int i = 0; i < size; i++) {
-            temp = temp.concat(integerData[i].toString());
-        }
-        return temp;
-    }
-
-    /**
-     * Overriden compareTo method that compares the calculated levenshtein distance between two IntegerLevenshtein objects
-     * @param otherInteger the object to be compared.
-     * @return The levenshtein distance between the two objects.
-     */
-    @Override
-    public int compareTo(IntegerLevenshtein otherInteger) {
-        LevenshteinDistance levenshtein = LevenshteinDistance.getDefaultInstance();
-        return levenshtein.apply(this.toString(), otherInteger.toString());
-    }
-}

src/main/java/com/cleverthis/interview/PadlockAdapter.java

@@ -1,47 +0,0 @@
-package com.cleverthis.interview;
-
-/**
- * This defines the interface that padlocks must conform to.
- * Concrete implementations will be adapted to this interface contract through concrete adapter classes.
- */
-public interface PadlockAdapter {
-
-    /**
-     * Get the size of the padlock's physical number pad
-     *
-     * @return A count of the physical buttons on the padlock
-     */
-    int getNumpadSize();
-
-    /**
-     *  Write key presses to the input buffer of the padlock
-     * @param address The position / index of the button that is pressed. For example, address 0 is the first button pressed.
-     * @param keyIndex The value of the button that is pressed. Cannot be greater than the numpad size, as the buttons increment
-     *                 sequentially
-     * @return The old value of keyIndex at the inputted address
-     */
-    Integer writeInputBuffer(int address, int keyIndex);
-
-    /**
-     * Check whether the inputted password is correct
-     * @return True if password is correct, false otherwise
-     */
-    boolean isPasscodeCorrect();
-
-    /**
-     * Returns the write counter
-     * @return The number of times a write operation has occurred
-     */
-    long getWriteCounter();
-
-    /**
-     * Returns the check counter
-     * @return The number of times the password has been checked for correctness
-     */
-    long getCheckCounter();
-
-    /**
-     * Resets both the check and write counters
-     */
-    void resetCounter();
-}

src/main/java/com/cleverthis/interview/PadlockJavaAdapter.java

@@ -1,49 +0,0 @@
-package com.cleverthis.interview;
-
-import com.cleverthis.interview.padlock.PadlockImpl;
-
-/**
- * The concrete implementation of PadlockAdapter that communicates with the padlock directly through a Java
- * class. This implementation also contains a cache that it keeps in sync with the underlying API, as a front-line
- * optimization against unnecessary write operations.
- */
-public class PadlockJavaAdapter extends PadlockImpl implements PadlockAdapter {
-    /**
-     * Intermediate cache between the underlying padlock API and any code that interfaces with the PadlockAdapter
-     * API.
-     */
-    private final Integer[] inputBufferState;
-
-    /**
-     * Create a padlock instance.
-     *
-     * @param numpadSize The number of buttons on the numpad of this lock.
-     */
-    public PadlockJavaAdapter(int numpadSize) {
-        super(numpadSize);
-
-        inputBufferState = new Integer[numpadSize];
-
-        for(int i = 0; i < this.getNumpadSize(); i++) {
-            inputBufferState[i] = i;
-            super.writeInputBuffer(i, i);
-        }
-    }
-
-    /**
-     * Writes to the underlying input buffer, but only if the cache shows that the write is necessary
-     * @param address The position / index of the button that is pressed. For example, address 0 is the first button pressed.
-     * @param keyIndex The value of the button that is pressed. Cannot be greater than the numpad size, as the buttons increment
-     *                 sequentially
-     * @return The old value that was replaced, which is the same as keyIndex if a write operation doesn't actually occur.
-     */
-    @Override
-    public Integer writeInputBuffer(int address, int keyIndex) {
-        if(inputBufferState[address] != keyIndex) {
-            inputBufferState[address] = keyIndex;
-            return super.writeInputBuffer(address, keyIndex);
-        } else {
-            return keyIndex;
-        }
-    }
-}

src/main/java/com/cleverthis/interview/Solution.java

@@ -0,0 +1,13 @@
+package com.cleverthis.interview;
+
+import com.cleverthis.interview.padlock.PadlockImpl;
+
+/**
+ * This is a placeholder class showing a simple boilerplate.
+ * This class is not required, so you can replace with your own architecture.
+ */
+public class Solution {
+    public void solve(PadlockImpl padlock) {
+        throw new RuntimeException("TODO");
+    }
+}

src/main/java/com/cleverthis/interview/SolverInterface.java

@@ -1,13 +0,0 @@
-package com.cleverthis.interview;
-
-/**
- * Interface that defines the class signature for solver implementations
- */
-public interface SolverInterface {
-
-    /**
-     * Solves the padlock passed in that conforms to the PadlockAdapter interface
-     * @param padlockAdapter the padlock object to solve
-     */
-    void solve(PadlockAdapter padlockAdapter);
-}

src/main/java/com/cleverthis/interview/WriteAwareBruteSolver.java

@@ -1,90 +0,0 @@
-package com.cleverthis.interview;
-
-import java.util.Iterator;
-import java.util.TreeSet;
-import org.apache.commons.text.similarity.LevenshteinDistance;
-
-/**
- * This is a write-aware brute solver implementation that uses the levenshtein distance to sort passcode permutations
- * into a tree. Walking the tree in-order (Likely a depth-first traversal internally) results in a naive nearest-neighbor
- * optimization that generally performs well, but may perform poorly in some cases. Heuristic solutions exist that have
- * acceptable performance, and this is a more naive heuristic implementation.
- *
- * This permutation optimization problem is NP-hard and can be represented as the traveling salesperson problem.
- * Representing passcode permutations as vertices and the levenshtein distance as edges in an undirected, weighted graph,
- * an optimal solution is the shortest path satisfying a tour of the entire graph.
- *
- * A more advanced solution (based on Christofides, or another TSP heuristic) may result in more performance gains, but
- * the performance of this nearest-neighbor solution is adequate for the keypad sizes under test. A keypad size of 9
- * results in a graph of vertex-count 9!. It's unlikely performance gains from a more intelligent TSP solver would
- * offset the performance cost of building a graph and optimizing traversal.
- */
-public class WriteAwareBruteSolver extends DumbBruteSolver {
-
-    private final TreeSet<IntegerLevenshtein> orderedTree;
-    private Integer numpadSize;
-
-    /**
-     * Creates an ordered tree on instantiation to be used as a cache for subsequent brute-force solves.
-     * @param numpadSize The size of the padlock's numpad, used in generation of the internal ordered tree
-     */
-    public WriteAwareBruteSolver(int numpadSize) {
-        orderedTree = new TreeSet<IntegerLevenshtein>();
-        this.numpadSize = numpadSize;
-
-        this.createOrderedTree(numpadSize);
-    }
-
-    /**
-     * Solves the padlock passed in to the method. The padlock's internal state should be correct after this method
-     * runs.
-     * @param padlockAdapter A padlock conforming to the PadlockAdapter contract
-     */
-    @Override
-    public void solve(PadlockAdapter padlockAdapter) {
-        int padlockNumpadSize = padlockAdapter.getNumpadSize();
-
-        if (this.numpadSize != padlockNumpadSize) {
-            this.createOrderedTree(padlockNumpadSize);
-        }
-
-        for (IntegerLevenshtein integerLevenshtein : orderedTree) {
-            if (this.checkPermutation(integerLevenshtein.getIntegerData(), padlockAdapter)) {
-                return;
-            }
-        }
-    }
-
-    /**
-     * Returns the size of the tree (the number of possible permutations)
-     * @return the size of the ordered tree
-     */
-    public Integer getTreeSize() {
-        return this.orderedTree.size();
-    }
-
-    /**
-     * Creates an ordered tree of possible passcode permutations
-     * @param size The number of keys on the numpad
-     */
-    protected void createOrderedTree(int size) {
-        if(this.numpadSize != size) {
-            this.numpadSize = size;
-            orderedTree.clear();
-        }
-
-        Integer[] currentPermutation = new Integer[numpadSize];
-        for(int i = 0; i < numpadSize; i++) {
-            currentPermutation[i] = i;
-        }
-
-        boolean morePermutationsExist = true;
-
-        do {
-            IntegerLevenshtein levenshteinPermutation = new IntegerLevenshtein(numpadSize);
-            levenshteinPermutation.setIntegerData(currentPermutation);
-            orderedTree.add(levenshteinPermutation);
-            morePermutationsExist = this.calculateNextPermutation(currentPermutation, numpadSize);
-        } while(morePermutationsExist);
-    }
-}

src/test/java/com/cleverthis/interview/DumbBruteSolverTest.java

@@ -1,102 +0,0 @@
-package com.cleverthis.interview;
-
-import org.junit.jupiter.api.Test;
-
-import static org.junit.jupiter.api.Assertions.*;
-
-/**
- * Tests for DumbBruteSolver class
- *
- * Tests that lexicographically ordered permutations are properly calculated, and that the solver works
- */
-public class DumbBruteSolverTest extends SolutionTestBase {
-
-    /**
-     * Overridden method that tests in SolutionTestBase.class expect defined and calls.
-     * Creates a DumbBruteSolver and calls the solve() method.
-     * @param padlock The padlock to solve
-     */
-    @Override
-    protected void solve(PadlockAdapter padlock) {
-        new DumbBruteSolver().solve(padlock);
-    }
-    /**
-     * Check whether a 7-button padlock can be solved
-     */
-    @Test
-    protected void testSolver() {
-        DumbBruteSolver dumbSolver = new DumbBruteSolver();
-        PadlockJavaAdapter padlock = new PadlockJavaAdapter(7);
-
-        dumbSolver.solve(padlock);
-
-        assertTrue(padlock.isPasscodeCorrect());
-    }
-
-    /**
-     * Check whether the next permutation is calculated correctly
-     */
-    @Test
-    protected void testOnePermutation() {
-        DumbBruteSolver dumbSolver = new DumbBruteSolver();
-
-        Integer[] permutation = new Integer[] {1, 2, 3, 4};
-        Integer[] correctPermutation = new Integer[] {1, 2, 4, 3};
-
-        dumbSolver.calculateNextPermutation(permutation, 4);
-
-        assertArrayEquals(permutation, correctPermutation);
-    }
-
-    /**
-     * Check whether two consecutive permutations are correct
-     */
-    @Test
-    protected void testTwoPermutations() {
-        DumbBruteSolver dumbSolver = new DumbBruteSolver();
-
-        Integer[] permutation = new Integer[] {1, 2, 3, 4};
-        Integer[] correctPermutation = new Integer[] {1, 3, 2, 4};
-
-        for(int i = 0; i < 2; i++) {
-            dumbSolver.calculateNextPermutation(permutation, 4);
-        }
-
-        assertArrayEquals(permutation, correctPermutation);
-    }
-
-    /**
-     * Check whether 23 consecutive permutations are correct
-     */
-    @Test
-    protected void test23Permutations() {
-        DumbBruteSolver dumbSolver = new DumbBruteSolver();
-
-        Integer[] permutation = new Integer[] {1, 2, 3, 4};
-        Integer[] correctPermutation = new Integer[] {4, 3, 2, 1};
-
-        for(int i = 0; i < 23; i++) {
-            dumbSolver.calculateNextPermutation(permutation, 4);
-        }
-
-        assertArrayEquals(permutation, correctPermutation);
-    }
-
-    /**
-     * Check whether the 24th permutation returns false, signifying we've exhausted all possible permutations
-     * for a list of size 4
-     */
-    @Test
-    protected void test24Permutations() {
-        DumbBruteSolver dumbSolver = new DumbBruteSolver();
-
-        Integer[] permutation = new Integer[] {1, 2, 3, 4};
-
-        for(int i = 0; i < 23; i++) {
-            assertTrue(dumbSolver.calculateNextPermutation(permutation, 4));
-        }
-
-        assertFalse(dumbSolver.calculateNextPermutation(permutation, 4));
-
-    }
-}

src/test/java/com/cleverthis/interview/PerformanceAnalyze.java

@@ -1,51 +0,0 @@
-package com.cleverthis.interview;
-
-import com.cleverthis.interview.padlock.PadlockImpl;
-
-/**
- * Performance test but not mean to run in unit test.
- */
-public class PerformanceAnalyze {
-
-    private static final int TOTAL_RUN = 500;
-    private static final int NUMPAD_SIZE = 9;
-    /**
-     * The solver object reference is held between tests, because the data structure used for optimization does not
-     * change between runs and keeping it in memory greatly increases performance.
-     */
-    static WriteAwareBruteSolver solver = new WriteAwareBruteSolver(NUMPAD_SIZE);
-
-    private static void solve(PadlockAdapter padlock) {
-        solver.solve(padlock);
-    }
-
-    static {
-        System.out.println("Total run: " + TOTAL_RUN);
-        System.out.println("Numpad size: " + NUMPAD_SIZE);
-    }
-
-    public static void main(String[] args) {
-        long timeSum = 0;
-        long writeSum = 0;
-        for (int i = 0; i < TOTAL_RUN; i++) {
-            PadlockAdapter padlock = new PadlockJavaAdapter(NUMPAD_SIZE);
-            padlock.resetCounter();
-            long start = System.currentTimeMillis();
-            solve((PadlockAdapter) padlock);
-            long end = System.currentTimeMillis();
-            if (!padlock.isPasscodeCorrect()) throw new IllegalStateException(
-                    "Invalid solution: passcode not correct after return");
-            long dT = end - start;
-            timeSum += dT;
-            writeSum += padlock.getWriteCounter();
-            System.out.println("Run #" + (i + 1) + ": time: " + dT + "ms; write: " + padlock.getWriteCounter());
-        }
-        System.out.println("Run time sum: " + timeSum + "ms");
-        System.out.println("Write sum: " + writeSum);
-        double avgTime = timeSum / (double) TOTAL_RUN;
-        double avgWrite = writeSum / (double) TOTAL_RUN;
-        System.out.println("Avg run time: " + avgTime + "ms");
-        System.out.println("Avg write: " + avgWrite);
-        System.out.println("Calculated estimate avg run time: " + (avgTime / 1000 + avgTime) + "s");
-    }
-}

src/test/java/com/cleverthis/interview/SolutionTest.java

@@ -0,0 +1,30 @@
+package com.cleverthis.interview;
+
+import com.cleverthis.interview.padlock.PadlockImpl;
+import org.junit.jupiter.api.Test;
+
+import java.util.Random;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * This is a simple placeholder to show how unit test works.
+ * You can replace it with your own test.
+ */
+class SolutionTest {
+    private void solve(PadlockImpl padlock) {
+        new Solution().solve(padlock);
+    }
+
+    @Test
+    void verify(){
+        Random random = new Random();
+        PadlockImpl padlock = new PadlockImpl(random.nextInt(1, 8));
+
+        long startTime = System.currentTimeMillis();
+        solve(padlock);
+        long endTime = System.currentTimeMillis();
+        assertTrue(padlock.isPasscodeCorrect());
+        System.out.println("Time usage: " + (endTime - startTime) + "ms");
+    }
+}

src/test/java/com/cleverthis/interview/SolutionTestBase.java

@@ -1,34 +0,0 @@
-package com.cleverthis.interview;
-
-import com.cleverthis.interview.padlock.PadlockImpl;
-import org.junit.jupiter.api.Test;
-
-import static org.junit.jupiter.api.Assertions.assertTrue;
-
-/**
- * This is a base class for verifying the correctness of the solution.
- */
-public abstract class SolutionTestBase {
-    
-    /**
-     * Implement your solution in this function.
-     * */
-    protected abstract void solve(PadlockAdapter padlock);
-
-    protected void verify(int numpadSize) {
-        PadlockAdapter padlock = new PadlockJavaAdapter(numpadSize);
-        solve(padlock);
-        assertTrue(padlock.isPasscodeCorrect());
-    }
-
-    /**
-     * Tests padlocks with numpad sizes of 1 to 7. This test runs for every class that extends this SolutionTestBase
-     * abstract class.
-     */
-    @Test
-    void verify1to7() {
-        for (int i = 1; i <= 7; i++) {
-            verify(i);
-        }
-    }
-}

src/test/java/com/cleverthis/interview/WriteAwareBruteSolverTest.java

@@ -1,55 +0,0 @@
-package com.cleverthis.interview;
-
-import org.junit.jupiter.api.Test;
-
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertTrue;
-
-/**
- * Tests for WriteAwareBruteSolver class
- *
- * These tests do not keep a long-lived reference to WriteAwareBruteSolver, instead opting
- * to reconstruct the permutation tree for every test. This is a trade-off between performance
- * and avoiding any inadvertent behavior changes from state persisting between tests.
- */
-public class WriteAwareBruteSolverTest extends SolutionTestBase {
-
-    /**
-     * Overridden method that tests in SolutionTestBase.class expect defined and calls.
-     * Creates a WriteAwareBruteSolver and calls the solve() method.
-     * @param padlock The padlock to solve
-     */
-    @Override
-    protected void solve(PadlockAdapter padlock) {
-        new WriteAwareBruteSolver(padlock.getNumpadSize()).solve(padlock);
-    }
-
-    /**
-     * Tests whether the solver can brute-force a 7-numpad padlock.
-     */
-    @Test
-    protected void testSolver() {
-        Integer numpadSize = 7;
-        WriteAwareBruteSolver writeAwareSolver = new WriteAwareBruteSolver(numpadSize);
-        PadlockJavaAdapter padlock = new PadlockJavaAdapter(numpadSize);
-
-        writeAwareSolver.solve(padlock);
-
-        assertTrue(padlock.isPasscodeCorrect());
-    }
-
-    /**
-     * Tests whether a numpad-size of 4 is correctly expanded to 24 possible permutations in the underlying
-     * tree
-     */
-    @Test
-    protected void testTreeSize() {
-        Integer numpadSize = 4;
-        WriteAwareBruteSolver writeAwareSolver = new WriteAwareBruteSolver(numpadSize);
-        PadlockJavaAdapter padlock = new PadlockJavaAdapter(4);
-
-        writeAwareSolver.solve(padlock);
-
-        assertEquals(writeAwareSolver.getTreeSize(), 24);
-    }
-}