题解报告：hdu 2141 Can you find it?（二分）

Problem Description

Give you three sequences of numbers A, B, C, then we give you a number X. Now you need to calculate if you can find the three numbers Ai, Bj, Ck, which satisfy the formula Ai+Bj+Ck = X.

Input

There are many cases. Every data case is described as followed: In the first line there are three integers L, N, M, in the second line there are L integers represent the sequence A, in the third line there are N integers represent the sequences B, in the forth line there are M integers represent the sequence C. In the fifth line there is an integer S represents there are S integers X to be calculated. 1<=L, N, M<=500, 1<=S<=1000. all the integers are 32-integers.

Output

For each case, firstly you have to print the case number as the form "Case d:", then for the S queries, you calculate if the formula can be satisfied or not. If satisfied, you print "YES", otherwise print "NO".

Sample Input

3 3 3

1 2 3

1 2 3

1 2 3

3

1

4

10

Sample Output

Case 1:

NO

YES

NO

解题思路：典型的二分搜索，先将a、b两两求和并排好序，然后二分搜索是否能找到x-c[j]这个值即可。 

AC代码(358ms)：

 #include<bits/stdc++.h>
 using namespace std;
 const int maxn=;
 int l,n,m,q,cnt=,x,a[maxn],b,c[maxn];bool flag;
 vector<int> vec;
 int main(){
     while(~scanf("%d%d%d",&l,&n,&m)){
         vec.clear();
         for(int i=;i<=l;++i)scanf("%d",&a[i]);
         for(int i=;i<=n;++i){
             scanf("%d",&b);
             for(int j=;j<=l;++j)
                 vec.push_back(a[j]+b);
         }
         sort(vec.begin(),vec.end());
         for(int i=;i<=m;++i)scanf("%d",&c[i]);
         scanf("%d",&q);printf("Case %d:\n",cnt++);
         while(q--){
             scanf("%d",&x);flag=false;
             for(int j=;j<=m;++j){
                 int pos=lower_bound(vec.begin(),vec.end(),x-c[j])-vec.begin();
                 if(pos!=l*n&&vec[pos]==x-c[j]){flag=true;break;}
             }
             if(flag)puts("YES");
             else puts("NO");
         }
     }
     return ;
 }