Add word search solution

Author: JAEKWANG97

word-search/jaekwang97.java

@@ -0,0 +1,55 @@
+class Solution {
+
+    static int[] dx = {0, 1, 0, -1};
+    static int[] dy = {1, 0, -1, 0};
+    static int n, m;
+
+    public boolean exist(char[][] board, String word) {
+        m = board[0].length;
+        n = board.length;
+
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                if (board[i][j] != word.charAt(0)) continue;
+
+                char cur = board[i][j];
+                board[i][j] = '#';
+                boolean flag = dfs(board, word, 1, i, j);
+                board[i][j] = cur;
+
+                if (flag) return true;
+            }
+        }
+
+        return false;
+    }
+
+    private static boolean dfs(
+        char[][] board,
+        String word,
+        int idx,
+        int x,
+        int y
+    ) {
+        if (idx == word.length()) return true;
+
+        for (int i = 0; i < 4; i++) {
+            int nx = x + dx[i];
+            int ny = y + dy[i];
+
+            if (nx < 0 || nx >= n || ny < 0 || ny >= m) continue;
+            if (board[nx][ny] != word.charAt(idx)) continue;
+
+            char cur = board[nx][ny];
+            board[nx][ny] = '#';
+
+            boolean flag = dfs(board, word, idx + 1, nx, ny);
+
+            board[nx][ny] = cur;
+
+            if (flag) return true;
+        }
+
+        return false;
+    }
+}