CUBE-T170: Cupid

#include <bits/stdc++.h>
using namespace std;

const int N = 1000;

int boys[N + 1], girls[N + 1];

int main(){

    int nCity, dist;
    scanf("%d%d", &nCity, &dist);
    for(int i = 1; i <= nCity; ++i){
        scanf("%d%d", &boys[i], &girls[i]);
    }
    for(int i = 1; i <= nCity; ++i){
        int upb = min(nCity, i + dist);
        for(int j = max(1, i - dist); j <= upb; ++j){
            if(boys[i] >= girls[j]){
                boys[i] -= girls[j];
                girls[j] = 0;
            } else {
                girls[j] -= boys[i];
                boys[i] = 0;
            }
        }
        if(boys[i] > 0){
            cout << "NO";
            return 0;
        }
    }
    for(int i = 1; i <= nCity; ++i){
        if(girls[i] > 0){
            cout << "NO";
            return 0;
        }
    }
    cout << "YES";

    return 0;
}