SDUT Greatest Number

转载于 2019-01-11 00:30:16 发布 · 65 阅读

本文介绍了一个算法挑战，任务是在给定的整数集合中找到不超过特定上限的最大四数之和。通过枚举所有可能的组合并进行优化，文章提供了一种有效的解决方案来找出所谓的GreatestNumber。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

Greatest Number

Time Limit: 1000MS Memory limit: 65536K

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<M≤ 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

示例输出

Case 1: 8

提示

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
#include<algorithm>

using namespace std;

int n,m;
int num[1000010];

int main(){

    //freopen("input.txt","r",stdin);

    int cases=0;
    while(~scanf("%d%d",&n,&m)){
        if(n==0 && m==0)
            break;
        num[0]=0;
        for(int i=1;i<=n;i++){
            scanf("%d",&num[i]);
            if(num[i]>m)
                i--,n--;
        }
        int cnt=n+1;
        for(int i=1;i<=n;i++)
            for(int j=i;j<=n;j++)
                if(num[i]+num[j]<=m)
                    num[cnt++]=num[i]+num[j];
        sort(num,num+cnt);
        int max=0,l,r=cnt-1,cur=cnt-1;
        for(int i=0;i<cnt;i++){
            l=i;
            while(l<=r){
                int mid=(l+r)>>1;
                int tmp=num[i]+num[mid];
                if(tmp>m)
                    r=mid-1;
                else if(tmp<m){
                    l=mid+1;
                    if(max<tmp){
                        cur=mid;
                        max=tmp;
                    }
                }else{
                    max=m;
                    i=cnt;
                    break;
                }
            }
            r=cur;
        }
        printf("Case %d: %d\n",++cases,max);
        printf("\n");
    }
    return 0;
}