# BZOJ 1634: [Usaco2007 Jan]Protecting the Flowers 护花(贪心)

Posted by 111qqz on Thursday, April 7, 2016

## 1634: [Usaco2007 Jan]Protecting the Flowers 护花

Time Limit: 5 Sec  Memory Limit: 64 MB Submit: 605  Solved: 383 [Submit][Status][Discuss]

## Description

Farmer John went to cut some wood and left N (2 <= N <= 100,000) cows eating the grass, as usual. When he returned, he found to his horror that the cows were in his garden eating his beautiful flowers. Wanting to minimize the subsequent damage, FJ decided to take immediate action and transport the cows back to their barn. Each cow i is at a location that is Ti minutes (1 <= Ti <= 2,000,000) away from the barn. Furthermore, while waiting for transport, she destroys Di (1 <= Di <= 100) flowers per minute. No matter how hard he tries,FJ can only transport one cow at a time back to the barn. Moving cow i to the barn requires 2*Ti minutes (Ti to get there and Ti to return). Write a program to determine the order in which FJ should pick up the cows so that the total number of flowers destroyed is minimized.

## Input

• Line 1: A single integer

N * Lines 2..N+1: Each line contains two space-separated integers, Ti and Di, that describe a single cow's characteristics

## Output

• Line 1: A single integer that is the minimum number of destroyed flowers

## Sample Input

6 3 1 2 5 2 3 3 2 4 1 1 6

86

## HINT

``````/* ***********************************************
Author :111qqz
Created Time :2016年04月07日 星期四 13时32分09秒
File Name :code/bzoj/1634.cpp
************************************************ */

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <cmath>
#include <cstdlib>
#include <ctime>
#define fst first
#define sec second
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define ms(a,x) memset(a,x,sizeof(a))
typedef long long LL;
#define pi pair < int ,int >
#define MP make_pair

using namespace std;
const double eps = 1E-8;
const int dx4[4]={1,0,0,-1};
const int dy4[4]={0,-1,1,0};
const int inf = 0x3f3f3f3f;
const int N=1E5+7;
int n;
struct node
{
LL t,d;

bool operator < (node b)const
{
return t*2LL*b.d<b.t*2LL*d;
}
}a[N];
int main()
{
#ifndef  ONLINE_JUDGE
freopen("code/in.txt","r",stdin);
#endif

ios::sync_with_stdio(false);
cin>>n ;
LL total = 0LL ;
for ( int i = 0 ; i < n ; i++) cin>>a[i].t>>a[i].d , total+=a[i].d;
sort(a,a+n);

LL ans = 0LL ;

for ( int i = 0  ; i < n ; i++ )
{
total-=a[i].d;
ans += total*2LL*a[i].t;
}

cout<< ans << endl ;
#ifndef ONLINE_JUDGE
fclose(stdin);
#endif
return 0;
}
``````