Greatest Number 山东省第一届省赛

Greatest Number

Time Limit: 1000ms   Memory limit: 65536K  有疑问？点这里^_^

题目描述

Saya likes math, because she think math can make her cleverer.
One day, Kudo invited a very simple game:
Given N
integers, then the players choose no more than four integers from them
(can be repeated) and add them together. Finally, the one whose sum is
the largest wins the game. It seems very simple, but there is one more
condition: the sum shouldn’t larger than a number M.
Saya
is very interest in this game. She says that since the number of
integers is finite, we can enumerate all the selecting and find the
largest sum. Saya calls the largest sum Greatest Number (GN). After
reflecting for a while, Saya declares that she found the GN and shows
her answer.
Kudo wants to know whether Saya’s answer is the best, so she comes to you for help.
Can you help her to compute the GN?

输入

The input consists of several test cases.
The first line of input in each test case contains two integers N (0<N≤1000) and M(0 1000000000), which represent the number of integers and the upper bound.
Each of the next N lines contains the integers. (Not larger than 1000000000)
The last case is followed by a line containing two zeros.

输出

For each case, print the case number (1, 2 …) and the GN.
Your output format should imitate the sample output. Print a blank line after each test case.

示例输入

2 10
100
2

0 0

示例输出

Case 1: 8
解题：先循环一下，两个两个的相加一下，然后二分查找，时间算好，不会超过1s；

 #include<iostream>
 #include<algorithm>
 #include<cstring>
 #include<cstdio>
 using namespace std;
 const int N = 1e6+;
 #define LL long long
 LL sum[N];
 LL a[N];
 int search(int l,int r,LL num)
 {
     int mid;
     while(l<r)
     {
         mid = (l+r)/;
         if(sum[mid]<=num) l = mid+;
         else  r  =  mid;
     }
     return l-;
 }
 int main()
 {
     int m,k,cnt = ;
     LL x,n;
     //freopen("greatest.in","r",stdin);
     while(scanf("%d %lld",&m,&n) && m+n)
     {
         k = ;
         for(int i=;i<=m;i++)
         {
             scanf("%lld",&x);
             if(x<=n)
                 a[k++] = x;
         }
         a[k]=;
         int kk = ;
         for(int i=;i<=k;i++)
             for(int j=;j<=k;j++)
            {
              if(a[i] + a[j] <=n)
                 sum[kk++] = a[i]+a[j];
            }
         sort(sum,sum+kk);
         LL ans = ;
         for(int i=;i<kk;i++)
         {
             LL M = n - sum[i];
             int x = search(,kk,M);
             ans = max(ans,sum[i]+sum[x]);
         }
         printf("Case %d: %lld\n\n",cnt++,ans);
     }
     return ;
 }