粮草|贪心

废话少说，上代码

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
struct Farmer{
    int price;
    int amount;
};
bool compare(const Farmer& a,const Farmer& b){
    return a.price<b.price;
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int n=0,m=0;
    cin>>n>>m;
    vector<Farmer> farmers(m);
    for(int i=0;i<m;++i)
        cin>>farmers[i].price>>farmers[i].amount;
    // 按单价从小到大排序 
    sort(farmers.begin(),farmers.end(),compare);
    long long total_cost=0;
    int remaining=n;
    for(int i=0;i<m&&remaining>0;++i) {
        if(farmers[i].amount>=remaining){
            // 当前农户的粮草足够满足剩余需求
            total_cost+=(long long)remaining*farmers[i].price;
            remaining=0;
        }else{
            // 购买当前农户的所有粮草 
            total_cost+=(long long)farmers[i].amount*farmers[i].price;
            remaining-=farmers[i].amount;
        }
    }
    cout<<total_cost;
    return 0;
}