便于理解的

#include<iostream>
#include<algorithm>
using namespace std;
struct Apple{
    int height;
    int need_energy;
    bool can_picked=false;//这个苹果能摘得到吗？
}apple[5001];

bool cmp(Apple a,Apple b){
    return a.need_energy<b.need_energy;
}
int main(){
    int n;
    int k;//还剩的力气
    cin>>n>>k;

    int a,b;
    cin>>a>>b;

    int he_can_hide=a+b;//小码王可以摘到的最大高度

    for(int i=1;i<=n;i++){
        cin>>apple[i].height;
        cin>>apple[i].need_energy;
        apple[i].can_picked = (he_can_hide>=apple[i].height);
    }
    
    sort(apple+1,apple+n+1,cmp);
    
    int cnt=0;//摘了几个了

    int i=1;
    while(i<=n&&k>0){
        if(apple[i].can_picked==true){
            if(k>=apple[i].need_energy){
                k-=apple[i].need_energy;
                cnt++;
            }
        }
        ++i;
    }
    //用for()也可以
    cout<<cnt;
    return 0;
}