Ìîäóëü: C++. Ñîðòèðîâêà ñ êîìïàðàòîðîì

#include<algorithm>
#include<iostream>
#include<cstdio>
#include<vector>
#include<cmath>
using namespace std;

struct sand {
    int cost, weight;
    double cw;

    sand() { }
    
    sand(int _cost, int _weight) {
        this->cost = _cost;
        this->weight = _weight;
        this->cw = 1. * _cost / _weight;
    }
};

bool cmp(sand a, sand b) {    

}

vector<sand>sandArray(0);
int n;
int w;
double answer;

int main() {
    cin >> n >> w;
    sandArray.resize(n);
    for (int i = 0; i < n; i++) {
        int cost, weight;
        cin >> cost >> weight;
        sandArray.at(i) = sand(cost, weight);
    }

    sort(sandArray.begin(), sandArray.end(), cmp);

    for (int i = 0; i < n; i++)
        if (sandArray.at(i).weight <= w) {
            w -= sandArray.at(i).weight;
            answer += sandArray.at(i).cost;
        }
        else {
            answer += sandArray.at(i).cw * w;
            w = 0;
        }
        
    printf("%.4lf", answer);
}