很简单的dfs；
1 class Solution { 2 public: 3 bool exist(vector<vector<char> > &board, string word) { 4 // Start typing your C/C++ solution below 5 // DO NOT write int main() function 6 if (word.empty()) { 7 return true; 8 } 9 if (board.empty()) { 10 return false; 11 } 12 int m = board.size(); 13 int n = board[0].size(); 14 if (word.size() > m * n) { 15 return false; 16 } 17 vector<vector<bool> > visited(m, vector<bool>(n, false)); 18 for (int i = 0; i < m; ++i) { 19 for (int j = 0; j < n; ++j) { 20 if (dfs(board, visited, word, i, j, 0)) { 21 return true; 22 } 23 } 24 } 25 return false; 26 } 27 bool dfs(vector<vector<char> > &board, vector<vector<bool> > &visited, string &word, int r, int c, int k) { 28 if (r < 0 || r >= board.size() || c < 0 || c >= board[0].size() || visited[r][c]) { 29 return false; 30 } 31 if (k == word.size() - 1) { 32 return (board[r][c] == word[k]); 33 } 34 if (board[r][c] != word[k]) { 35 return false; 36 } 37 visited[r][c] = true; 38 bool res = dfs(board, visited, word, r - 1, c, k + 1) || dfs(board, visited, word, r + 1, c, k + 1) || dfs(board, visited, word, r, c - 1, k + 1) || dfs(board, visited, word, r, c + 1, k + 1); 39 visited[r][c] = false; 40 return res; 41 } 42 };