leetcode 79

DFS 四个方向分别search通过vis数组标记走过的点，若最后找到则返回true

bool DFS(int i,int j,vector<vector<char>>& board, string word,vector<vector<int>>& vis,int level)
    {
        if(level==word.size())return true;
        else{
            int m = board.size();
            int n = board[0].size();
            if(i<0||j<0||i>=m||j>=n||vis[i][j]==1||board[i][j]!=word[level])return false;
            vis[i][j]=1;
            bool res=    (DFS(i-1,j,board,word,vis,level+1)||
                          DFS(i+1,j,board,word,vis,level+1)||
                          DFS(i,j-1,board,word,vis,level+1)||
                          DFS(i,j+1,board,word,vis,level+1));
            vis[i][j]=0;
            return res;
        }
    }
    bool exist(vector<vector<char>>& board, string word) {
        int m = board.size();
        int n = board[0].size();
        vector<vector<int>> vis(m,vector<int>(n,0));
        for(int i=0;i<board.size();i++)
            for(int j=0;j<board[0].size();j++)
                if(DFS(i,j,board,word,vis,0))return true;
        return false;
    }