梅开二度

bfs 死循环

#include<bits/stdc++.h>
using namespace std;
int n;
pair<int,int> beginning,ending;
int dx[] = {1,0,-1,0};
int dy[] = {0,1,0,-1};
bool s[1005][1005];
bool isgo[1005][1005];

bool check(int x,int y){
    if (x <= 0 || x >= n || y <= 0 || y >= n || !(s[x][y]) || isgo[x][y]){
        return false;
    }return true;
}

int bfs(){
    int cnt = 0;
    queue<pair<int,int>> q;
    q.push(make_pair(beginning.first,beginning.second));
    while (q.size() != 0){
        pair<int,int> f = q.front();
        q.pop();
        if (f == ending)return cnt;
        isgo[f.first][f.second] = true;
        for (int i=0;i<4;i++){
            if (check(f.first + dx[i],f.second + dy[i])){
                q.push({f.first+dx[i],f.second + dy[i]});
            }
        }
        cnt++;
    }
}

int main(){
    cin >> n;
    for (int i=1;i<=n;i++){
        for (int j=1;j<=n;j++){
            int v;cin >> v;
            if (v == 1)s[i][j] = false;
            else s[i][j] = true;
        }
    }
    cin >> beginning.first >> beginning.second;
    cin >> ending.first >> ending.second;
    cout << bfs();
    return 0;
}