求助！！c语言编程求解。

1. 题目描述： 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
2. 解答要求： 语言：C，时间限制：1000ms, 内存限制：64MB。
3. 输入： 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.

4. 输出：
   For each S, a single line containing d, or a single line containing “no solution”.

5. 样例
   输入样例
   5
   2
   3
   5
   7
   12
   5
   2
   16
   64
   256
   1024
   0
   输出样例
   12
   no solution

#include<stdio.h>
#include<string.h>
#include<algorithm>
#define INF -0x3f3f3f3f
using namespace std;
int a[1010];
int main()
{
    int n;
    int i,j;
    while(scanf("%d",&n),n)
    {
        for(i=0;i<n;i++)
            scanf("%d",&a[i]);
        sort(a,a+n);
        int ans=INF;
        for(i=n-1;i>=0;i--)
        {
            for(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("no solution\n");
        else
            printf("%d\n",ans);
    }
    return 0;
}

http://www.voidcn.com/article/p-dquihsug-bs.html
http://www.bubuko.com/infodetail-1473358.html