add: Word Search solution

Author: JEONGBEOMKO

word-search/JEONGBEOMKO.java

@@ -0,0 +1,43 @@
+public class Solution {
+    /*
+    time complexity: O(M × N × 3^L)
+    space complexity: O(M × N + L)
+    */
+    private int rows, cols;
+    private boolean[][] visited;
+    private final int[] dx = {0, 1, 0, -1};
+    private final int[] dy = {1, 0, -1, 0};
+
+    public boolean exist(char[][] board, String word) {
+        rows = board.length;
+        cols = board[0].length;
+        visited = new boolean[rows][cols];
+
+        for (int i = 0; i < rows; i++) {
+            for (int j = 0; j < cols; j++) {
+                if (dfs(board, word, i, j, 0)) {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    private boolean dfs(char[][] board, String word, int x, int y, int idx) {
+        if (idx == word.length()) return true;
+
+        if (x < 0 || y < 0 || x >= rows || y >= cols) return false;
+        if (visited[x][y] || board[x][y] != word.charAt(idx)) return false;
+
+        visited[x][y] = true;
+
+        for (int d = 0; d < 4; d++) {
+            if (dfs(board, word, x + dx[d], y + dy[d], idx + 1)) {
+                return true;
+            }
+        }
+
+        visited[x][y] = false; // 백트래킹
+        return false;
+    }
+}