刷题之单词搜索（leetcode）

很容易就想到回溯

class Solution {
private:
    int istrue = false;
    int dir[4][2] = { -1,0,0,-1,0,1,1,0 };
    void backtracking(vector<vector<char>>& board, string word, vector<vector<bool>>& visited, int x, int y, int index)
    {
        if (index == word.size())//当找全word的字母，则标记
        {
            istrue = true;
            return;
        }
        
        for (int i = 0; i < 4; i++)
        {
            int nextx = x + dir[i][0];
            int nexty = y + dir[i][1];
            if (nextx >= board.size() || nexty >= board[0].size() || nextx < 0 || nexty < 0)
                continue;
            if (visited[nextx][nexty] == false && board[nextx][nexty] == word[index])
            {
                visited[nextx][nexty] = true;
                backtracking(board, word, visited, nextx, nexty, index + 1);
                visited[nextx][nexty] = false;//回溯
            }
        }
    }
public:
    bool exist(vector<vector<char>>& board, string word) {
        vector<vector<bool>>visited(board.size(), vector<bool>(board[0].size(), false));
        for (int i = 0; i < board.size(); i++)
        {
            for (int j = 0; j < board[0].size(); j++)
            {
                //遍历所有字母,找到word中第一个字母，再进行深度优先搜索找word的其他字母
                if (board[i][j] == word[0])
                {
                    visited[i][j] = true;
                    backtracking(board, word, visited, i, j, 1);
                    visited[i][j] = false;//回溯
                    //一旦找到，直接返回
                    if(istrue)
                        return true;
                }
            }
        }
        return istrue;
    }
};
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