add solution of word-search

Author: jinhyungrhee

word-search/jinhyungrhee.java

@@ -0,0 +1,40 @@
+class Solution {
+    public boolean exist(char[][] board, String word) {
+
+        boolean[][] visited = new boolean[board.length][board[0].length];
+
+        for (int i = 0; i < board.length; i++) {
+            for (int j = 0; j < board[0].length; j++) {
+                if(dfs(board, word, visited, i, j, 0)) {
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    public boolean dfs(char[][] board, String word, boolean[][] visited, int x, int y, int index) {
+
+        // [성공] : 모든 글자 매칭 성공
+        if (index == word.length()) return true;
+
+        // [실패] : 범위 초과, 방문함, 글자 불일치
+        if (x < 0 || x >= board.length || y < 0 || y >= board[0].length ||
+                visited[x][y] || board[x][y] != word.charAt(index)) {
+            return false;
+        }
+
+        visited[x][y] = true;
+        int[][] dir = {{1, 0}, {-1, 0}, {0, -1}, {0, 1}};
+        for (int i = 0; i < 4; i++) {
+            int newX = x + dir[i][0], newY = y + dir[i][1];
+            if (dfs(board, word, visited, newX, newY, index + 1)) {
+                return true; // 찾았으면 바로 리턴
+            }
+        }
+        visited[x][y] = false; // backtrack
+
+        return false; // 4방향 다 실패하면 false
+
+    }
+}