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a8796ba886
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a8796ba886 | ||
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f360c538eb |
@ -1,15 +1,13 @@
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package com.cleverthis.interview;
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import java.util.Arrays;
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import java.util.Collection;
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import java.util.Collections;
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import java.util.List;
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import java.util.stream.Stream;
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/**
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* Brute-forces padlock using lexicographically ordered permutation generation
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* Brute-forces padlock using lexicographically ordered permutation generation.
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*
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* Algorithm documented at: https://en.wikipedia.org/wiki/Permutation#Generation_in_lexicographic_order
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* Permutation-generation algorithm documented at: https://en.wikipedia.org/wiki/Permutation#Generation_in_lexicographic_order
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*/
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public class DumbBruteSolver implements SolverInterface {
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@ -31,7 +29,7 @@ public class DumbBruteSolver implements SolverInterface {
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boolean isCorrect = checkPermutation(currentPermutation, padlockAdapter);
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if (!isCorrect) {
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boolean nextPermutationExists = calculateNextPermutation(currentPermutation, numpadSize);
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boolean nextPermutationExists = calculateNextPermutation(currentPermutation);
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if(!nextPermutationExists) {
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return;
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}
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@ -60,10 +58,11 @@ public class DumbBruteSolver implements SolverInterface {
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/**
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* Calculates the next permutation in lexicographic order, based on the algorithm linked on wikipedia
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* @param currentPermutation The current permutation to run the algorithm on
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* @param numpadSize The number of items in the set to be permuted
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* @return true if next permutation successfully generated, false if permutations have been exhausted
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*/
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protected boolean calculateNextPermutation(Integer[] currentPermutation, int numpadSize) {
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protected boolean calculateNextPermutation(Integer[] currentPermutation) {
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int numpadSize = currentPermutation.length;
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if(numpadSize < 2) { return false; }
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//Integer k, l;
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@ -3,7 +3,7 @@ package com.cleverthis.interview;
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import org.apache.commons.text.similarity.LevenshteinDistance;
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/**
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* A wrapper class that holds possible padlock passcode permutations in an integer array. This class
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* Holds a single possible padlock passcode permutation in an integer array. This class
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* overloads the toString() method and is comparable, using its string value to calculate the levenshtein distance and
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* use those distance values for sorting into a data structure.
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*/
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@ -50,7 +50,7 @@ public class IntegerLevenshtein implements Comparable<IntegerLevenshtein> {
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}
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/**
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* Overriden compareTo method that compares the calculated levenshtein distance between two IntegerLevenshtein objects
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* Overridden compareTo method that compares the calculated levenshtein distance between two IntegerLevenshtein objects
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* @param otherInteger the object to be compared.
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* @return The levenshtein distance between the two objects.
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*/
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@ -1,7 +1,7 @@
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package com.cleverthis.interview;
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/**
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* This defines the interface that padlocks must conform to.
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* This defines the contract that padlocks must conform to.
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* Concrete implementations will be adapted to this interface contract through concrete adapter classes.
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*/
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public interface PadlockAdapter {
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@ -1,7 +1,7 @@
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package com.cleverthis.interview;
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/**
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* Interface that defines the class signature for solver implementations
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* Defines the contract for padlock-cracking solver implementations
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*/
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public interface SolverInterface {
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@ -1,11 +1,9 @@
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package com.cleverthis.interview;
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import java.util.Iterator;
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import java.util.TreeSet;
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import org.apache.commons.text.similarity.LevenshteinDistance;
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/**
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* This is a write-aware brute solver implementation that uses the levenshtein distance to sort passcode permutations
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* A write-aware brute solver implementation that uses the levenshtein distance to sort passcode permutations
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* into a tree. Walking the tree in-order (Likely a depth-first traversal internally) results in a naive nearest-neighbor
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* optimization that generally performs well, but may perform poorly in some cases. Heuristic solutions exist that have
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* acceptable performance, and this is a more naive heuristic implementation.
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@ -17,7 +15,7 @@ import org.apache.commons.text.similarity.LevenshteinDistance;
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* A more advanced solution (based on Christofides, or another TSP heuristic) may result in more performance gains, but
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* the performance of this nearest-neighbor solution is adequate for the keypad sizes under test. A keypad size of 9
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* results in a graph of vertex-count 9!. It's unlikely performance gains from a more intelligent TSP solver would
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* offset the performance cost of building a graph and optimizing traversal.
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* offset the performance cost of building a graph and solving for an optimal tour.
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*/
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public class WriteAwareBruteSolver extends DumbBruteSolver {
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@ -68,10 +66,8 @@ public class WriteAwareBruteSolver extends DumbBruteSolver {
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* @param size The number of keys on the numpad
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*/
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protected void createOrderedTree(int size) {
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if(this.numpadSize != size) {
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this.numpadSize = size;
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orderedTree.clear();
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}
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this.numpadSize = size;
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orderedTree.clear();
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Integer[] currentPermutation = new Integer[numpadSize];
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for(int i = 0; i < numpadSize; i++) {
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@ -84,7 +80,7 @@ public class WriteAwareBruteSolver extends DumbBruteSolver {
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IntegerLevenshtein levenshteinPermutation = new IntegerLevenshtein(numpadSize);
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levenshteinPermutation.setIntegerData(currentPermutation);
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orderedTree.add(levenshteinPermutation);
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morePermutationsExist = this.calculateNextPermutation(currentPermutation, numpadSize);
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morePermutationsExist = this.calculateNextPermutation(currentPermutation);
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} while(morePermutationsExist);
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}
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}
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@ -43,7 +43,7 @@ public class DumbBruteSolverTest extends SolutionTestBase {
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Integer[] permutation = new Integer[] {1, 2, 3, 4};
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Integer[] correctPermutation = new Integer[] {1, 2, 4, 3};
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dumbSolver.calculateNextPermutation(permutation, 4);
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dumbSolver.calculateNextPermutation(permutation);
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assertArrayEquals(permutation, correctPermutation);
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}
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@ -59,7 +59,7 @@ public class DumbBruteSolverTest extends SolutionTestBase {
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Integer[] correctPermutation = new Integer[] {1, 3, 2, 4};
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for(int i = 0; i < 2; i++) {
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dumbSolver.calculateNextPermutation(permutation, 4);
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dumbSolver.calculateNextPermutation(permutation);
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}
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assertArrayEquals(permutation, correctPermutation);
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@ -76,7 +76,7 @@ public class DumbBruteSolverTest extends SolutionTestBase {
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Integer[] correctPermutation = new Integer[] {4, 3, 2, 1};
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for(int i = 0; i < 23; i++) {
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dumbSolver.calculateNextPermutation(permutation, 4);
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dumbSolver.calculateNextPermutation(permutation);
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}
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assertArrayEquals(permutation, correctPermutation);
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@ -93,10 +93,10 @@ public class DumbBruteSolverTest extends SolutionTestBase {
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Integer[] permutation = new Integer[] {1, 2, 3, 4};
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for(int i = 0; i < 23; i++) {
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assertTrue(dumbSolver.calculateNextPermutation(permutation, 4));
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assertTrue(dumbSolver.calculateNextPermutation(permutation));
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}
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assertFalse(dumbSolver.calculateNextPermutation(permutation, 4));
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assertFalse(dumbSolver.calculateNextPermutation(permutation));
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}
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}
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@ -1,7 +1,5 @@
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package com.cleverthis.interview;
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import com.cleverthis.interview.padlock.PadlockImpl;
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/**
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* Performance test but not mean to run in unit test.
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*/
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@ -1,6 +1,5 @@
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package com.cleverthis.interview;
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import com.cleverthis.interview.padlock.PadlockImpl;
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import org.junit.jupiter.api.Test;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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