Leetcode79. Word Search单词搜索

给定一个二维网格和一个单词，找出该单词是否存在于网格中。

单词必须按照字母顺序，通过相邻的单元格内的字母构成，其中“相邻”单元格是那些水平相邻或垂直相邻的单元格。同一个单元格内的字母不允许被重复使用。

示例:

board = [ ['A','B','C','E'], ['S','F','C','S'], ['A','D','E','E'] ] 给定 word = "ABCCED", 返回 true. 给定 word = "SEE", 返回 true. 给定 word = "ABCB", 返回 false.

class Solution {
public:
    vector<vector<int> > visit;
    int len;
    int r;
    int c;
    int dx[4] = {1, -1, 0, 0};
    int dy[4] = {0, 0, 1, -1};
    bool exist(vector<vector<char> >& board, string word)
    {
        len = word.size();
        if(len == 0)
            return true;
        r = board.size();
        if(r == 0)
            return false;
        c = board[0].size();
        if(r * c < len)
            return false;
        for(int i = 0; i < r; i++)
        {
            for(int j = 0; j < c; j++)
            {
                visit.clear();
                visit = vector<vector<int> >(r, vector<int>(c, 0));
                if(board[i][j] == word[0])
                {
                    visit[i][j] = 1;
                    if(DFS(board, 1, word, i, j))
                    return true;
                }
            }
        }
        return false;
    }

        bool DFS(vector<vector<char> >& board, int pos, string cmp, int x, int y)
        {
            if(pos >= cmp.size())
                return true;
            for(int i = 0; i < 4; i++)
            {
                int xx = x + dx[i];
                int yy = y + dy[i];
                if(xx < 0 || xx >= r || yy < 0 || yy >= c)
                    continue;
                if(visit[xx][yy] == 1)
                    continue;
                if(board[xx][yy] != cmp[pos])
                    continue;
                visit[xx][yy] = 1;
                if(DFS(board, pos + 1, cmp, xx, yy))
                    return true;
                visit[xx][yy] = 0;
            }
            return false;

        }
};