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HardvanHardvan
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Add CrosswordSolver algorithm (#5626)
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‎DIRECTORY.md

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* [AllPathsFromSourceToTarget](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/AllPathsFromSourceToTarget.java)
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* [ArrayCombination](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/ArrayCombination.java)
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* [Combination](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/Combination.java)
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* [CrosswordSolver](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/CrosswordSolver.java)
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* [FloodFill](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/FloodFill.java)
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* [KnightsTour](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/KnightsTour.java)
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* [MazeRecursion](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/MazeRecursion.java)
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* [AllPathsFromSourceToTargetTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/AllPathsFromSourceToTargetTest.java)
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* [ArrayCombinationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/ArrayCombinationTest.java)
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* [CombinationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/CombinationTest.java)
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* [CrosswordSolverTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/CrosswordSolverTest.java)
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* [FloodFillTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/FloodFillTest.java)
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* [KnightsTourTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/KnightsTourTest.java)
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* [MazeRecursionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/backtracking/MazeRecursionTest.java)

‎src/main/java/com/thealgorithms/backtracking/CrosswordSolver.java

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package com.thealgorithms.backtracking;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* A class to solve a crossword puzzle using backtracking.
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* Example:
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* Input:
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* puzzle = {
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* {' ', ' ', ' '},
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* {' ', ' ', ' '},
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* {' ', ' ', ' '}
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* }
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* words = List.of("cat", "dog")
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*
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* Output:
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* {
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* {'c', 'a', 't'},
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* {' ', ' ', ' '},
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* {'d', 'o', 'g'}
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* }
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*/
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public final class CrosswordSolver {
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private CrosswordSolver() {
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}
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/**
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* Checks if a word can be placed at the specified position in the crossword.
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*
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* @param puzzle The crossword puzzle represented as a 2D char array.
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* @param word The word to be placed.
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* @param row The row index where the word might be placed.
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* @param col The column index where the word might be placed.
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* @param vertical If true, the word is placed vertically; otherwise, horizontally.
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* @return true if the word can be placed, false otherwise.
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*/
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public static boolean isValid(char[][] puzzle, String word, int row, int col, boolean vertical) {
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for (int i = 0; i < word.length(); i++) {
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if (vertical) {
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if (row + i >= puzzle.length || puzzle[row + i][col] != ' ') {
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return false;
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}
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} else {
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if (col + i >= puzzle[0].length || puzzle[row][col + i] != ' ') {
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return false;
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}
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}
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}
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return true;
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}
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/**
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* Places a word at the specified position in the crossword.
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*
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* @param puzzle The crossword puzzle represented as a 2D char array.
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* @param word The word to be placed.
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* @param row The row index where the word will be placed.
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* @param col The column index where the word will be placed.
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* @param vertical If true, the word is placed vertically; otherwise, horizontally.
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*/
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public static void placeWord(char[][] puzzle, String word, int row, int col, boolean vertical) {
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for (int i = 0; i < word.length(); i++) {
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if (vertical) {
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puzzle[row + i][col] = word.charAt(i);
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} else {
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puzzle[row][col + i] = word.charAt(i);
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}
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}
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}
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/**
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* Removes a word from the specified position in the crossword.
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*
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* @param puzzle The crossword puzzle represented as a 2D char array.
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* @param word The word to be removed.
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* @param row The row index where the word is placed.
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* @param col The column index where the word is placed.
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* @param vertical If true, the word was placed vertically; otherwise, horizontally.
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*/
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public static void removeWord(char[][] puzzle, String word, int row, int col, boolean vertical) {
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for (int i = 0; i < word.length(); i++) {
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if (vertical) {
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puzzle[row + i][col] = ' ';
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} else {
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puzzle[row][col + i] = ' ';
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}
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}
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}
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/**
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* Solves the crossword puzzle using backtracking.
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*
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* @param puzzle The crossword puzzle represented as a 2D char array.
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* @param words The list of words to be placed.
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* @return true if the crossword is solved, false otherwise.
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*/
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public static boolean solveCrossword(char[][] puzzle, List<String> words) {
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// Create a mutable copy of the words list
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List<String> remainingWords = new ArrayList<>(words);
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for (int row = 0; row < puzzle.length; row++) {
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for (int col = 0; col < puzzle[0].length; col++) {
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if (puzzle[row][col] == ' ') {
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for (String word : new ArrayList<>(remainingWords)) {
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for (boolean vertical : new boolean[] {true, false}) {
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if (isValid(puzzle, word, row, col, vertical)) {
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placeWord(puzzle, word, row, col, vertical);
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remainingWords.remove(word);
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if (solveCrossword(puzzle, remainingWords)) {
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return true;
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}
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remainingWords.add(word);
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removeWord(puzzle, word, row, col, vertical);
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}
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}
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}
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return false;
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}
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}
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}
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return true;
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}
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}

‎src/test/java/com/thealgorithms/backtracking/CrosswordSolverTest.java

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package com.thealgorithms.backtracking;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertFalse;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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import java.util.Arrays;
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import java.util.List;
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import org.junit.jupiter.api.Test;
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public class CrosswordSolverTest {
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@Test
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public void testValidPlacement() {
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char[][] puzzle = {{' ', ' ', ' '}, {' ', ' ', ' '}, {' ', ' ', ' '}};
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assertTrue(CrosswordSolver.isValid(puzzle, "cat", 0, 0, true));
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assertTrue(CrosswordSolver.isValid(puzzle, "dog", 0, 0, false));
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assertFalse(CrosswordSolver.isValid(puzzle, "cat", 1, 2, false));
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}
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@Test
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public void testPlaceAndRemoveWord() {
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char[][] puzzle = {{' ', ' ', ' '}, {' ', ' ', ' '}, {' ', ' ', ' '}};
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CrosswordSolver.placeWord(puzzle, "cat", 0, 0, true);
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assertEquals('c', puzzle[0][0]);
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assertEquals('a', puzzle[1][0]);
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assertEquals('t', puzzle[2][0]);
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CrosswordSolver.removeWord(puzzle, "cat", 0, 0, true);
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assertEquals(' ', puzzle[0][0]);
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assertEquals(' ', puzzle[1][0]);
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assertEquals(' ', puzzle[2][0]);
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}
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@Test
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public void testSolveCrossword() {
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char[][] puzzle = {{' ', ' ', ' '}, {' ', ' ', ' '}, {' ', ' ', ' '}};
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List<String> words = Arrays.asList("cat", "dog", "car");
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assertTrue(CrosswordSolver.solveCrossword(puzzle, words));
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/* Solved crossword:
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* c d c
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* a o a
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* t g r
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*/
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assertEquals('c', puzzle[0][0]);
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assertEquals('a', puzzle[1][0]);
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assertEquals('t', puzzle[2][0]);
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assertEquals('d', puzzle[0][1]);
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assertEquals('o', puzzle[1][1]);
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assertEquals('g', puzzle[2][1]);
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assertEquals('c', puzzle[0][2]);
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assertEquals('a', puzzle[1][2]);
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assertEquals('r', puzzle[2][2]);
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}
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@Test
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public void testNoSolution() {
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char[][] puzzle = {{' ', ' ', ' '}, {' ', ' ', ' '}, {' ', ' ', ' '}};
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List<String> words = Arrays.asList("cat", "dog", "elephant"); // 'elephant' is too long for the grid
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assertFalse(CrosswordSolver.solveCrossword(puzzle, words));
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}
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}

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