题解 | 明日DISCO

#include <bits/stdc++.h>
using namespace std;
using ll = long long ;
int main() {
    int n;
    cin >> n;
    vector<vector<ll>>a(n + 10, vector<ll>(n + 10, 0));
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            cin >> a[i][j];
        }
    }
    for (int i = 1; i <= n; i++) {
        for (int j = 0; j <= n; j++) {
            if (a[i][j] == 0) {
                continue;
            }
            if (a[i - 1][j] >= 0 && a[i][j - 1] >= 0 && a[i + 1][j] >= 0 && a[i][j + 1] >= 0 &&
                    a[i][j] < 0) {
                a[i][j] = 0;
            }
            if (a[i - 1][j] <= 0 && a[i][j - 1] <= 0 && a[i + 1][j] <= 0 && a[i][j + 1] <= 0 &&
                    a[i][j] > 0) {
                a[i][j] = 0;
            }
        }
    }
    for(int i = 1; i<=n;i++){
        for(int j = 1;j<=n;j++){
            if(a[i][j]!=0){
                cout<<"NO";
                return 0;
            }
        }
    }
    cout<<"YES";
    return 0;
}