feat: 79. Word Search solution

Author: Yiseull

word-search/Yiseull.java

@@ -0,0 +1,35 @@
+class Solution {
+
+    private final int[] dx = {-1, 1, 0, 0};
+    private final int[] dy = {0, 0, -1, 1};
+
+    public boolean exist(char[][] board, String word) {
+        for (int i = 0; i < board.length; i++) {
+            for (int j = 0; j < board[0].length; j++) {
+                if (board[i][j] == word.charAt(0) && dfs(board, word, i, j, 1)) {
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+    private boolean dfs(char[][] board, String word, int x, int y, int index) {
+        if (index == word.length()) return true;
+
+        char tmp = board[x][y];
+        board[x][y] = '0';
+
+        for (int i = 0; i < 4; i++) {
+            int nextX = x + dx[i], nextY = y + dy[i];
+            if (0 <= nextX && nextX < board.length && 0 <= nextY && nextY < board[0].length && board[nextX][nextY] == word.charAt(index)) {
+                if(dfs(board, word, nextX, nextY, index + 1)) return true;
+            }
+        }
+
+        board[x][y] = tmp;
+
+        return false;
+    }
+}