本蒟蒻做这题卡了30多分钟

#include<bits/stdc++.h>
using namespace std;
#pragma G++ optimize(2)
int n,k,T;
int last,now;
bool f;
struct node{
    int day,t;
}a[100005];
bool cmp(node a,node b){
    return a.day < b.day;
}
int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	cin>>T;
	while(T--){
		cin>>n>>k;
		for(int i = 1;i <= n;i++){
			cin>>a[i].day>>a[i].t;
		}
		sort(a + 1,a + n + 1,cmp);
		for(int i = 1;i <= n;i++){
        	now += (a[i].day - a[i - 1].day) * k;
        	now -= a[i].t;
        	if(now < 0){
        		f = 1;
        		break;
			}
        }
        if(f == 1){
            f = 0;
            now = 0;
            cout<<"No\n";
            continue;
        }
        cout<<"Yes\n";
        now = 0;
	}
	return 0;
}

打代码打了30多分钟，然后全WA
真的无语了???

各位大佬帮本蒟蒻瞅一眼