模板：

vector<int> path;
    vector<vector<int>> result;
    void backTracking(......) {
        if (......) {
            ......
            return;
        }
        for (int i = 0; i < size; ++i) {
            path.emplace_back(......);
            backTracking(......);
            path.pop_back();
        }
    }
 

int nextP[4][2] = {{0,1},{1,0},{0,-1},{-1,0}};
class Solution {
public:
    bool flag = false;
    void dfs(vector<vector<char>>& board, string& word, vector<vector<bool>>& book,
             int row, int col, int curX, int curY, int wordindex)
    {
        if(wordindex == word.size())
        {
            flag = true;
        }
        for(int i = 0; i < 4; i++)
        {
            int newX = curX + nextP[i][0];
            int newY = curY + nextP[i][1];
            if(newX<0||newX>=row
            || newY<0||newY>=col)
                continue;
            if(book[newX][newY]==false && word[wordindex]==board[newX][newY])
            {
                book[curX][curY] = true; // 这次的dfs吸取教训只修改了值没有进行还原
                dfs(board, word, book, row, col, newX, newY, wordindex+1);
                book[curX][curY] = false; // fds回溯时一定要还原状态；
            }
        }
    }
    bool exist(vector<vector<char>>& board, string word) {
        int row = board.size();
        int col = board[0].size();
        for(int i = 0; i < row; i++)
        {
            for(int j = 0; j < col; j++)
            {
                if(board[i][j] == word[0])
                {
                    vector<vector<bool>> book(row, vector<bool>(col, false));
                    dfs(board, word, book, row, col, i, j, 1);
                    if(flag)
                        return true;
                }
            }
        }
        return false;
    }
};