PROG-1152: ไฟ (Fire)

#include <bits/stdc++.h>

using namespace std;
const int N = 1e3 + 10;
const int N2 = 2e3 + 10;
int ar[N][N];
vector <int> fire[N2];

int main(){

    int n;
    scanf("%d", &n);

    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            scanf("%d", &ar[i][j]);
            fire[i+j].push_back(ar[i][j]);
        }
    }

    int ans = 0;
    priority_queue <int> pq;
    for(int i=2*n;i>=3;i--){
        for(auto x: fire[i]){
            pq.push(x);
        }
        ans += pq.top();
        pq.pop();
    }

    printf("%d", ans);

    return 0;
}