HDU-2616

Kill the monster

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1525    Accepted Submission(s): 1043

Problem Description

There is a mountain near yifenfei’s hometown. On the mountain lived a big monster. As a hero in hometown, yifenfei wants to kill it. 
Now we know yifenfei have n spells, and the monster have m HP, when HP <= 0 meaning monster be killed. Yifenfei’s spells have different effect if used in different time. now tell you each spells’s effects , expressed (A ,M). A show the spell can cost A HP to monster in the common time. M show that when the monster’s HP <= M, using this spell can get double effect.

 

Input

The input contains multiple test cases.
Each test case include, first two integers n, m (2<n<10, 1<m<10^7), express how many spells yifenfei has.
Next n line , each line express one spell. (Ai, Mi).(0<Ai,Mi<=m).

 

Output

For each test case output one integer that how many spells yifenfei should use at least. If yifenfei can not kill the monster output -1.

 

Sample Input

3 100

10 20

45 89

5 40

 

3 100

10 20

45 90

5 40

 

 

3 100

10 20

45 84

5 40

 

Sample Output

3

2

-1

题意：

有n个符咒，怪兽有m点血。每个符咒有两个属性：

1.伤害A；

2.在怪物血量低于M时造成2*A点伤害。

AC代码：

 #include<bits/stdc++.h>
 using namespace std;

 struct node{
     int x,y;
 }a[];

 bool vis[];
 int n,m,ans;

 void dfs(int m,int len){
     if(len>=ans)
         return;
     if(m<=){
         ans=min(ans,len);
         return;
     }
     for(int i=;i<n;i++){
         if(vis[i]==){
             vis[i]=;
             if(m<=a[i].y)
             dfs(m-*a[i].x,len+);
             else
             dfs(m-a[i].x,len+);
             vis[i]=;
         }
     }
 }

 int main(){
     while(cin>>n>>m){
         for(int i=;i<n;i++){
             cin>>a[i].x>>a[i].y;
         }
         memset(vis,,sizeof(vis));
         ans=;
         dfs(m,);
         if(ans>){
             cout<<-<<endl;
         }
         else{
             cout<<ans<<endl;
         }
     }
     return ;
 }