题目：

题解：

class Solution {
public:bool exist(vector<vector<char>>& board, string word) {rows = board.size();cols = board[0].size();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:int rows, cols;bool dfs(vector<vector<char>>& board, string word, int i, int j, int k) {if (i >= rows || i < 0 || j >= cols || j < 0 || board[i][j] != word[k]) return false;if (k == word.size() - 1) return true;board[i][j] = '\0';bool res = dfs(board, word, i + 1, j, k + 1) || dfs(board, word, i - 1, j, k + 1) || dfs(board, word, i, j + 1, k + 1) || dfs(board, word, i , j - 1, k + 1);board[i][j] = word[k];return res;}
};