K - Hero

        这个题目也算考察贪心算法,如何攻击对方英雄使得自己的hp会减少最低,一开始我是想到先攻击输出高的,如果输出同样高则攻击血量少的,但是很不幸,WA,然后看了别人的是优先攻击血量少而且攻击高的(难道这就是我王者荣耀只有黄金水平的原因),所以使用了dsp/hp的方法来排序,但是值得注意的是,输入的是int类型,在“/”的时候如果不转换为double类型会造成精度丢失,继而GG,继续WA,然后这个题目学到了sort的第三个参数的用法,自定义排序,这么好用的参数我怎么现在才发现呢,这很C++。


Description

When playing DotA with god-like rivals and pig-like team members, you have to face an embarrassing situation: All your teammates are killed, and you have to fight 1vN. 

There are two key attributes for the heroes in the game, health point (HP) and damage per shot (DPS). Your hero has almost infinite HP, but only 1 DPS. 

To simplify the problem, we assume the game is turn-based, but not real-time. In each round, you can choose one enemy hero to attack, and his HP will decrease by 1. While at the same time, all the lived enemy heroes will attack you, and your HP will decrease by the sum of their DPS. If one hero's HP fall equal to (or below) zero, he will die after this round, and cannot attack you in the following rounds. 

Although your hero is undefeated, you want to choose best strategy to kill all the enemy heroes with minimum HP loss.
 

Input

The first line of each test case contains the number of enemy heroes N (1 <= N <= 20). Then N lines followed, each contains two integers DPSi and HPi, which are the DPS and HP for each hero. (1 <= DPSi, HPi <= 1000)
 

Output

Output one line for each test, indicates the minimum HP loss.
 

Sample Input

1
10 2
2
100 1
1 100
 

Sample Output

20
201



下面是代码:


#include <iostream>
#include <algorithm>
using namespace std;
class Enemy
{
public:
    int  dps;
    int  hp;
    Enemy(int edps=0, int ehp=0):dps(edps),hp(ehp){}
};
const int maxn=20;
int n;
int myhp, alldps;
Enemy enemy[maxn];
void Init()
{
    int dpsi, hpi;
    myhp=0;
    alldps=0;
    for(int i=0;i<n;i++)
    {
        cin>>dpsi>>hpi;
        enemy[i]=Enemy(dpsi, hpi);  //敌人对象化
        alldps+=dpsi;               //计算所有敌人的伤害值
    }
}
bool compare(Enemy a, Enemy b)
{
    ///优先攻击血量少攻击高的英雄
    return (double)a.dps/(double)a.hp>(double)b.dps/(double)b.hp;
}
void Attack()
{
    ///攻击英雄,按照compare的顺序
    for(int ai=0;ai<n;ai++)
    {
        myhp+=enemy[ai].hp*alldps;    //攻击敌人
        alldps-=enemy[ai].dps;      //敌人死亡
    }
}
int main()
{
    while(cin>>n)
    {
        Init();
        sort(enemy, enemy+n, compare);
        Attack();
        cout<<myhp<<endl;
    }
    return 0;
}