题解 | 上三角矩阵判定

#include <iostream>
#include <vector>

using namespace std;

int main() 
{
    int n = 0;
    vector< vector <int> > a;//定义二维向量
    
    cin>>n;
    a.resize(n);//初始化行
    for (int i1 = 0;i1 <= n-1;i1++)
    {
        a[i1].resize(n);//初始化列
    }

    for (int j = 0;j <= n-1;j++)
    {
        for (int j1 = 0;j1 <= n-1;j1++)
        {
            cin>>a[j][j1];
        }
    }
    
    for (int i2 = 1;i2 <= n-1;i2++)
    {
        for (int i3 = 0;i3 <= i2-1;i3++)
        {
            if (a[i2][i3] != 0)
            {
                cout<<"NO"<<endl;
                return 0;
            }
        }
    }
    cout<<"YES"<<endl;
    return 0;
}