poj--2549--Sumsets（二分查找）

Sumsets

Time Limit: 1000MS

Memory Limit: 65536KB

64bit IO Format: %I64d & %I64u

Submit Status

Description

Given S, a set of integers, find the largest d such that a + b + c = d where a, b, c, and d are distinct elements of S.

Input

Several S, each consisting of a line containing an integer 1 <= n <= 1000 indicating the number of elements in S, followed by the elements of S, one per line. Each element of S is a distinct integer between -536870912 and +536870911 inclusive. The last line of input contains 0.

Output

For each S, a single line containing d, or a single line containing "no solution".

Sample Input

5
2 
3 
5 
7 
12
5
2 
16 
64 
256 
1024
0

Sample Output

12
no solution

Source

Waterloo local 2001.06.02

/*在数列中找四个数使a+b+c=d;转化之后得a+b=d-c,先对数列排序列举每一个d-c，
二分查找a和b*/
#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
#define MAX 100100
#define INF -0x3f3f3f
int a[MAX];
int main()
{
	int n;
	while(scanf("%d",&n),n)
	{
		for(int i=0;i<n;i++)
		scanf("%d",&a[i]);
		sort(a,a+n);
		int ans=INF;
		for(int i=n-1;i>=0;i--)
		{
			for(int j=n-1;j>=0;j--)
			{
				if(i==j)
				continue;
				int sum=a[i]-a[j];
				int l=0,r=j-1;
				while(l<r)
				{
					if(a[l]+a[r]==sum)
					{
						ans=a[i];
						break;
					}
					 if(a[l]+a[r]>sum)
					r--;
					else 
					l++;
				}
				if(ans!=INF) break;
			}
			if(ans!=INF) break;
		}
		if(ans!=INF)
		printf("%d\n",ans);
		else
		printf("no solution\n");
	}
	return 0;
}