AtCoder Beginner Contest 085 D Katana Thrower （贪心+计算机除法特性）

Problem Statement

You are going out for a walk, when you suddenly encounter a monster. Fortunately, you have N katana (swords), Katana 1, Katana 2, …, Katana N, and can perform the following two kinds of attacks in any order:

Wield one of the katana you have. When you wield Katana i (1≤i≤N), the monster receives ai points of damage. The same katana can be wielded any number of times.

Throw one of the katana you have. When you throw Katana i (1≤i≤N) at the monster, it receives bi points of damage, and you lose the katana. That is, you can no longer wield or throw that katana.

The monster will vanish when the total damage it has received is H points or more. At least how many attacks do you need in order to vanish it in total?

Constraints

1≤N≤105

1≤H≤109

1≤ai≤bi≤109

All input values are integers.

Input

Input is given from Standard Input in the following format:

N H

a1 b1

:

aN bN

Output

Print the minimum total number of attacks required to vanish the monster.

Sample Input 1

1 10

3 5

Sample Output 1

3

You have one katana. Wielding it deals 3 points of damage, and throwing it deals 5 points of damage. By wielding it twice and then throwing it, you will deal 3+3+5=11 points of damage in a total of three attacks, vanishing the monster.

Sample Input 2

2 10

3 5

2 6

Sample Output 2

2

In addition to the katana above, you also have another katana. Wielding it deals 2 points of damage, and throwing it deals 6 points of damage. By throwing both katana, you will deal 5+6=11 points of damage in two attacks, vanishing the monster.

Sample Input 3

4 1000000000

1 1

1 10000000

1 30000000

1 99999999

Sample Output 3

860000004

Sample Input 4

5 500

35 44

28 83

46 62

31 79

40 43

Sample Output 4

9

题意：给n个宝剑，h的生命值，给出n个宝剑的砍伤害和扔伤害，砍可以砍无数次，扔只能一次并且扔完之后不能再用此剑砍。

思路：贪心：找出砍的最大伤害，然后在扔伤害中，找出比砍伤害大的个数，总伤害减去所有的扔伤害之后，判断怪兽是否死亡，为死亡再计算用多少此砍伤害

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <set>
#include <string>
#include <cstring>
#include <cmath>
#include <map>
#include <stack>
#define N 100005
using namespace std;
typedef long long ll;
ll a
,b
,sumb
= {0};
int main()
{

ll n,y;
while(scanf("%lld%lld",&n,&y)==2)
{
ll imax=-111111,sum=0;
for(int i=1; i<=n; i++)
{
scanf("%lld%lld",&a[i],&b[i]);
if(a[i]>imax)
imax=a[i];
}
int num=0;
sort(b+1,b+1+n);
for(int i=n; i>=1; i--)
{
if(imax<=b[i]&&y>0)
{
y=y-b[i];
num++;
}
}
y=y-sum;
int r=y/imax;
if(r>0)
{
if(r*imax<y)
r++;
num+=r;
}
printf("%d\n",num);
}

}