[leetcode]Word Search

枚举开始位置,DFS验证

const int dx[] = {0,0,1,-1};
const int dy[] = {1,-1,0,0};
class Solution {
public:
    unordered_set<long long> flag;
    bool check(vector<vector<char> > & board , string& word , int x , int y , int pos){
        if(pos == word.size()) return true;
        for(int i = 0 ; i < 4 ; i++){
            int tx = x + dx[i];
            int ty = y + dy[i];
            if(tx >= 0 && tx < board.size() && ty >= 0 && ty < board[tx].size()){
                if(flag.find(tx*100000+ty) == flag.end() && board[tx][ty] == word[pos]){
                    flag.insert(tx*100000+ty);
                    if(check(board , word , tx , ty , pos + 1)){
                        return true;
                    }else{
                        flag.erase(tx*100000+ty);
                    }
                }
            }
        }
        return false;
    }
    bool exist(vector<vector<char> > &board, string word) {
        if(word == "") return true;
        int size = board.size();
        
        for(int i = 0 ; i < size ; i++){
            for(int j = 0 ; j < board[i].size() ; j++){
                if(board[i][j] == word[0]){
                    flag.clear();
                    flag.insert(i*100000 + j);
                    if(check(board , word , i , j , 1)) return true;
                }
            }
        }
        return false;
    }
};