Add Word Seach - algorithm

Author: Ojasvix20

Java/algorithms/matrix/WordSearch.java

@@ -0,0 +1,113 @@
+/*
+ * Algorithm Name: Word Search
+ * Programming Language: Java
+ * Category: Matrix, Backtracking, Depth-First Search (DFS)
+ * Difficulty Level: Hard
+ *
+ * Author: Ojasvi Bakshi
+ *
+ * Algorithm Description:
+ * Given an m x n grid of characters and a string "word", this algorithm returns true
+ * if the word exists in the grid. The word can be constructed from letters of sequentially
+ * adjacent cells, where "adjacent" cells are horizontally or vertically neighboring.
+ * The same letter cell may not be used more than once.
+ *
+ * Time Complexity: O(N * 3^L), where N is the number of cells and L is the length
+ * of the word. For each cell, we branch out, but we don't go back, so there are 3 choices.
+ * Space Complexity: O(L) for the recursion stack depth.
+ */
+package DSA_Code.Java.algorithms.matrix;
+
+import java.util.Scanner;
+
+public class WordSearch {
+
+    public static boolean exist(char[][] board, String word) {
+        if (board == null || board.length == 0 || word == null || word.length() == 0) {
+            return false;
+        }
+
+        int m = board.length;
+        int n = board[0].length;
+
+        for (int i = 0; i < m; i++) {
+            for (int j = 0; j < n; j++) {
+                // Start the search only if the first character matches
+                if (board[i][j] == word.charAt(0)) {
+                    if (search(board, word, i, j, 0)) {
+                        return true;
+                    }
+                }
+            }
+        }
+        return false;
+    }
+
+    private static boolean search(char[][] board, String word, int r, int c, int index) {
+        // Base Case 1: Success - we've found all characters in the word
+        if (index == word.length()) {
+            return true;
+        }
+
+        // Base Case 2: Failure - out of bounds or character mismatch
+        if (r < 0 || c < 0 || r >= board.length || c >= board[0].length || board[r][c] != word.charAt(index)) {
+            return false;
+        }
+
+        // Mark the current cell as visited to avoid reusing it
+        char temp = board[r][c];
+        board[r][c] = '#';
+
+        // Explore neighbors (up, down, left, right)
+        boolean found = search(board, word, r + 1, c, index + 1) ||
+                        search(board, word, r - 1, c, index + 1) ||
+                        search(board, word, r, c + 1, index + 1) ||
+                        search(board, word, r, c - 1, index + 1);
+
+        // Backtrack: un-mark the cell, restoring it for other paths
+        board[r][c] = temp;
+
+        return found;
+    }
+
+
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+
+        System.out.print("Enter number of rows: ");
+        int m = sc.nextInt();
+        System.out.print("Enter number of columns: ");
+        int n = sc.nextInt();
+
+        char[][] board = new char[m][n];
+
+        System.out.println("Enter grid characters:");
+        for (int i = 0; i < m; i++) {
+            for (int j = 0; j < n; j++) {
+                board[i][j] = sc.next().charAt(0);
+            }
+        }
+        
+        System.out.print("\nEnter the word to search for: ");
+        String word = sc.next();
+
+        System.out.println("\nOriginal Grid:");
+        for (char[] row : board) {
+            for (char cell : row) {
+                System.out.print(cell + " ");
+            }
+            System.out.println();
+        }
+
+        // Apply the algorithm
+        boolean found = exist(board, word);
+
+        if (found) {
+            System.out.println("\nThe word \"" + word + "\" was found in the grid. ✅");
+        } else {
+            System.out.println("\nThe word \"" + word + "\" was not found in the grid. ❌");
+        }
+
+        sc.close();
+    }
+}