部分揹包問題（挖

#include <algorithm>
#include <stdio.h>
using namespace std;

struct bag {
	double w;
	double v;
	double wv;
};

bool cmp(bag a, bag b) {
	return a.wv > b.wv;
}

int main() {
	int n, m;
	scanf("%d%d", &n, &m);
	struct bag a[n];
	for (int i = 0; i < n; i++) {
		scanf("%lf%lf", &a[i].w, &a[i].v);
		a[i].wv = a[i].v / a[i].w;
	}
	sort(a, a + n, cmp);
	int i = 0;
	double jb = 0;
	while (m > 0) {
		if (m >= a[i].w) {
			m -= a[i].w;
			jb += a[i].v;
			i++;
		} else {
			jb += (double)m * a[i].wv;
			m = 0;
		}
	}
	printf("%.2lf", jb);
	return 0;
}