#include

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
struct mooncake {
  float mount, price, unit;
};
int cmp(mooncake a, mooncake b) {
  return a.unit > b.unit;
}
int main() {
//读取月饼信息，并按价格排序
  int n, need;
  cin >> n >> need;
  vector<mooncake> a(n);
  for (int i = 0; i < n; i++)  cin>>a[i].mount;
  for (int i = 0; i < n; i++)  cin>>a[i].price;
  for (int i = 0; i < n; i++) a[i].unit = a[i].price / a[i].mount;
  sort(a.begin(), a.end(), cmp);
//计算价格
  float result = 0.0;
  for (int i = 0; i < n; i++) {
    if (a[i].mount <= need) {
      result = result + a[i].price;
    }
    else {
      result = result + a[i].unit * need;
      break;
    }
    need = need - a[i].mount;
  }
  printf("%.2f", result);
  return 0;
}

一开始没想到用结构做，用了2个分开的数组来存月饼的价格和数量，到了排序时发现会麻烦。

排序好了后，后面的价格计算比较简单，就用总需求和月饼数量依次比较。