Merge branch 'master' into jobscheduling_deadline_new_algo

Author: siriak

DIRECTORY.md

@@ -63,7 +63,7 @@
         <plugins>
             <plugin>
                 <artifactId>maven-surefire-plugin</artifactId>
-                <version>3.5.0</version>
+                <version>3.5.1</version>
                 <configuration>
                     <forkNode implementation="org.apache.maven.plugin.surefire.extensions.SurefireForkNodeFactory"/>
                 </configuration>

pom.xml

@@ -0,0 +1,124 @@
+package com.thealgorithms.backtracking;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A class to solve a crossword puzzle using backtracking.
+ * Example:
+ * Input:
+ *  puzzle = {
+ *      {' ', ' ', ' '},
+ *      {' ', ' ', ' '},
+ *      {' ', ' ', ' '}
+ *  }
+ *  words = List.of("cat", "dog")
+ *
+ * Output:
+ *  {
+ *      {'c', 'a', 't'},
+ *      {' ', ' ', ' '},
+ *      {'d', 'o', 'g'}
+ *  }
+ */
+public final class CrosswordSolver {
+    private CrosswordSolver() {
+    }
+
+    /**
+     * Checks if a word can be placed at the specified position in the crossword.
+     *
+     * @param puzzle   The crossword puzzle represented as a 2D char array.
+     * @param word     The word to be placed.
+     * @param row      The row index where the word might be placed.
+     * @param col      The column index where the word might be placed.
+     * @param vertical If true, the word is placed vertically; otherwise, horizontally.
+     * @return true if the word can be placed, false otherwise.
+     */
+    public static boolean isValid(char[][] puzzle, String word, int row, int col, boolean vertical) {
+        for (int i = 0; i < word.length(); i++) {
+            if (vertical) {
+                if (row + i >= puzzle.length || puzzle[row + i][col] != ' ') {
+                    return false;
+                }
+            } else {
+                if (col + i >= puzzle[0].length || puzzle[row][col + i] != ' ') {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    /**
+     * Places a word at the specified position in the crossword.
+     *
+     * @param puzzle   The crossword puzzle represented as a 2D char array.
+     * @param word     The word to be placed.
+     * @param row      The row index where the word will be placed.
+     * @param col      The column index where the word will be placed.
+     * @param vertical If true, the word is placed vertically; otherwise, horizontally.
+     */
+    public static void placeWord(char[][] puzzle, String word, int row, int col, boolean vertical) {
+        for (int i = 0; i < word.length(); i++) {
+            if (vertical) {
+                puzzle[row + i][col] = word.charAt(i);
+            } else {
+                puzzle[row][col + i] = word.charAt(i);
+            }
+        }
+    }
+
+    /**
+     * Removes a word from the specified position in the crossword.
+     *
+     * @param puzzle   The crossword puzzle represented as a 2D char array.
+     * @param word     The word to be removed.
+     * @param row      The row index where the word is placed.
+     * @param col      The column index where the word is placed.
+     * @param vertical If true, the word was placed vertically; otherwise, horizontally.
+     */
+    public static void removeWord(char[][] puzzle, String word, int row, int col, boolean vertical) {
+        for (int i = 0; i < word.length(); i++) {
+            if (vertical) {
+                puzzle[row + i][col] = ' ';
+            } else {
+                puzzle[row][col + i] = ' ';
+            }
+        }
+    }
+
+    /**
+     * Solves the crossword puzzle using backtracking.
+     *
+     * @param puzzle The crossword puzzle represented as a 2D char array.
+     * @param words  The list of words to be placed.
+     * @return true if the crossword is solved, false otherwise.
+     */
+    public static boolean solveCrossword(char[][] puzzle, List<String> words) {
+        // Create a mutable copy of the words list
+        List<String> remainingWords = new ArrayList<>(words);
+
+        for (int row = 0; row < puzzle.length; row++) {
+            for (int col = 0; col < puzzle[0].length; col++) {
+                if (puzzle[row][col] == ' ') {
+                    for (String word : new ArrayList<>(remainingWords)) {
+                        for (boolean vertical : new boolean[] {true, false}) {
+                            if (isValid(puzzle, word, row, col, vertical)) {
+                                placeWord(puzzle, word, row, col, vertical);
+                                remainingWords.remove(word);
+                                if (solveCrossword(puzzle, remainingWords)) {
+                                    return true;
+                                }
+                                remainingWords.add(word);
+                                removeWord(puzzle, word, row, col, vertical);
+                            }
+                        }
+                    }
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+}

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

@@ -1,152 +1,125 @@
 package com.thealgorithms.backtracking;
 
+/**
+ * This class contains methods to solve a maze using recursive backtracking.
+ * The maze is represented as a 2D array where walls, paths, and visited/dead
+ * ends are marked with different integers.
+ *
+ * The goal is to find a path from a starting position to the target position
+ * (map[6][5]) while navigating through the maze.
+ */
 public final class MazeRecursion {
+
     private MazeRecursion() {
     }
 
-    public static void mazeRecursion() {
-        // First create a 2 dimensions array to mimic a maze map
-        int[][] map = new int[8][7];
-        int[][] map2 = new int[8][7];
-
-        // We use 1 to indicate wall
-        // Set the ceiling and floor to 1
-        for (int i = 0; i < 7; i++) {
-            map[0][i] = 1;
-            map[7][i] = 1;
-        }
-
-        // Then we set the left and right wall to 1
-        for (int i = 0; i < 8; i++) {
-            map[i][0] = 1;
-            map[i][6] = 1;
-        }
-
-        // Now we have created a maze with its wall initialized
-
-        // Here we set the obstacle
-        map[3][1] = 1;
-        map[3][2] = 1;
-
-        // Print the current map
-        System.out.println("The condition of the map： ");
-        for (int i = 0; i < 8; i++) {
-            for (int j = 0; j < 7; j++) {
-                System.out.print(map[i][j] + " ");
-            }
-            System.out.println();
-        }
-
-        // clone another map for setWay2 method
-        for (int i = 0; i < map.length; i++) {
-            System.arraycopy(map[i], 0, map2[i], 0, map[i].length);
-        }
-
-        // By using recursive backtracking to let your ball(target) find its way in the
-        // maze
-        // The first parameter is the map
-        // Second parameter is x coordinate of your target
-        // Third parameter is the y coordinate of your target
-        setWay(map, 1, 1);
-        setWay2(map2, 1, 1);
-
-        // Print out the new map1, with the ball footprint
-        System.out.println("After the ball goes through the map1，show the current map1 condition");
-        for (int i = 0; i < 8; i++) {
-            for (int j = 0; j < 7; j++) {
-                System.out.print(map[i][j] + " ");
-            }
-            System.out.println();
+    /**
+     * This method solves the maze using the "down -> right -> up -> left"
+     * movement strategy.
+     *
+     * @param map The 2D array representing the maze (walls, paths, etc.)
+     * @return The solved maze with paths marked, or null if no solution exists.
+     */
+    public static int[][] solveMazeUsingFirstStrategy(int[][] map) {
+        if (setWay(map, 1, 1)) {
+            return map;
         }
+        return null;
+    }
 
-        // Print out the new map2, with the ball footprint
-        System.out.println("After the ball goes through the map2，show the current map2 condition");
-        for (int i = 0; i < 8; i++) {
-            for (int j = 0; j < 7; j++) {
-                System.out.print(map2[i][j] + " ");
-            }
-            System.out.println();
+    /**
+     * This method solves the maze using the "up -> right -> down -> left"
+     * movement strategy.
+     *
+     * @param map The 2D array representing the maze (walls, paths, etc.)
+     * @return The solved maze with paths marked, or null if no solution exists.
+     */
+    public static int[][] solveMazeUsingSecondStrategy(int[][] map) {
+        if (setWay2(map, 1, 1)) {
+            return map;
         }
+        return null;
     }
 
     /**
-     * Using recursive path finding to help the ball find its way in the maze
-     * Description：
-     * 1. map (means the maze)
-     * 2. i, j (means the initial coordinate of the ball in the maze)
-     * 3. if the ball can reach the end of maze, that is position of map[6][5],
-     * means the we have found a path for the ball
-     * 4. Additional Information： 0 in the map[i][j] means the ball has not gone
-     * through this position, 1 means the wall, 2 means the path is feasible, 3
-     * means the ball has gone through the path but this path is dead end
-     * 5. We will need strategy for the ball to pass through the maze for example:
-     * Down -> Right -> Up -> Left, if the path doesn't work, then backtrack
+     * Attempts to find a path through the maze using a "down -> right -> up -> left"
+     * movement strategy. The path is marked with '2' for valid paths and '3' for dead ends.
      *
-     * @author OngLipWei
-     * @version Jun 23, 2021 11:36:14 AM
-     * @param map The maze
-     * @param i   x coordinate of your ball(target)
-     * @param j   y coordinate of your ball(target)
-     * @return If we did find a path for the ball，return true，else false
+     * @param map The 2D array representing the maze (walls, paths, etc.)
+     * @param i   The current x-coordinate of the ball (row index)
+     * @param j   The current y-coordinate of the ball (column index)
+     * @return True if a path is found to (6,5), otherwise false
      */
-    public static boolean setWay(int[][] map, int i, int j) {
-        if (map[6][5] == 2) { // means the ball find its path, ending condition
+    private static boolean setWay(int[][] map, int i, int j) {
+        if (map[6][5] == 2) {
             return true;
         }
-        if (map[i][j] == 0) { // if the ball haven't gone through this point
-            // then the ball follows the move strategy : down -> right -> up -> left
-            map[i][j] = 2; // we assume that this path is feasible first, set the current point to 2
-                           // first。
-            if (setWay(map, i + 1, j)) { // go down
+
+        // If the current position is unvisited (0), explore it
+        if (map[i][j] == 0) {
+            // Mark the current position as '2'
+            map[i][j] = 2;
+
+            // Move down
+            if (setWay(map, i + 1, j)) {
                 return true;
-            } else if (setWay(map, i, j + 1)) { // go right
+            }
+            // Move right
+            else if (setWay(map, i, j + 1)) {
                 return true;
-            } else if (setWay(map, i - 1, j)) { // go up
+            }
+            // Move up
+            else if (setWay(map, i - 1, j)) {
                 return true;
-            } else if (setWay(map, i, j - 1)) { // go left
+            }
+            // Move left
+            else if (setWay(map, i, j - 1)) {
                 return true;
-            } else {
-                // means that the current point is the dead end, the ball cannot proceed, set
-                // the current point to 3 and return false, the backtracking will start, it will
-                // go to the previous step and check for feasible path again
-                map[i][j] = 3;
-                return false;
             }
-        } else { // if the map[i][j] != 0 , it will probably be 1,2,3, return false because the
-            // ball cannot hit the wall, cannot go to the path that has gone though before,
-            // and cannot head to deadened.
+
+            map[i][j] = 3; // Mark as dead end (3) if no direction worked
             return false;
         }
+        return false;
     }
 
-    // Here is another move strategy for the ball: up->right->down->left
-    public static boolean setWay2(int[][] map, int i, int j) {
-        if (map[6][5] == 2) { // means the ball find its path, ending condition
+    /**
+     * Attempts to find a path through the maze using an alternative movement
+     * strategy "up -> right -> down -> left".
+     *
+     * @param map The 2D array representing the maze (walls, paths, etc.)
+     * @param i   The current x-coordinate of the ball (row index)
+     * @param j   The current y-coordinate of the ball (column index)
+     * @return True if a path is found to (6,5), otherwise false
+     */
+    private static boolean setWay2(int[][] map, int i, int j) {
+        if (map[6][5] == 2) {
             return true;
         }
-        if (map[i][j] == 0) { // if the ball haven't gone through this point
-            // then the ball follows the move strategy : up->right->down->left
-            map[i][j] = 2; // we assume that this path is feasible first, set the current point to 2
-                           // first。
-            if (setWay2(map, i - 1, j)) { // go up
+
+        if (map[i][j] == 0) {
+            map[i][j] = 2;
+
+            // Move up
+            if (setWay2(map, i - 1, j)) {
                 return true;
-            } else if (setWay2(map, i, j + 1)) { // go right
+            }
+            // Move right
+            else if (setWay2(map, i, j + 1)) {
                 return true;
-            } else if (setWay2(map, i + 1, j)) { // go down
+            }
+            // Move down
+            else if (setWay2(map, i + 1, j)) {
                 return true;
-            } else if (setWay2(map, i, j - 1)) { // go left
+            }
+            // Move left
+            else if (setWay2(map, i, j - 1)) {
                 return true;
-            } else {
-                // means that the current point is the dead end, the ball cannot proceed, set
-                // the current point to 3 and return false, the backtracking will start, it will
-                // go to the previous step and check for feasible path again
-                map[i][j] = 3;
-                return false;
             }
-        } else { // if the map[i][j] != 0 , it will probably be 1,2,3, return false because the
-            // ball cannot hit the wall, cannot go to the path that has gone through before,
-            // and cannot head to deadend.
+
+            map[i][j] = 3; // Mark as dead end (3) if no direction worked
             return false;
         }
+        return false;
     }
 }