poj 3262

贪心法的精髓在于只考虑局部最优

#include <iostream>
#include <cstdio>
#include <iomanip>
#include <string>
#include <cstdlib>
#include <cstring>
#include <queue>
#include <set>
#include <vector>
#include <map>
#include <algorithm>
#include <cmath>
#include <stack>
#include <stdlib.h>
#include <stdio.h>

#define INF 0x3f3f3f3f
#define LINF 0x3f3f3f3f3f3f3f3f
#define ll long long
#define ull unsigned long long
#define uint unsigned int
#define l(x) x<<1
#define r(x) x<<1|1
#define ms(a,b) memset(a,b,sizeof(a))

using namespace std;

struct node {
	int len, val;
	double k;
};
bool cmp(const node&a, const node&b) {
	return a.len * b.val < b.len * a.val;
}

int n,sum,ans;
node d[111111];

int main() {
	ios::sync_with_stdio(false);

	sum = ans = 0;
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> d[i].len >> d[i].val;
		d[i].k = 1.0 * d[i].val / d[i].len;
		sum += d[i].val;
	}

	sort(d, d + n, cmp);

	for (int i = 0; i < n; i++) {
		sum -= d[i].val;
		ans += d[i].len * 2 * sum;
	}

	cout << ans << endl;
	return 0;
}