Sumsets（4sum问题）

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Sumsets

Time Limit: 1000MS Memory Limit: 65536KTotal Submissions: 8954 Accepted: 2465

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

52 3 5 7 1252 16 64 256 10240

Sample Output

12no solution

Source

Waterloo local 2001.06.02

这里是4sum问题或者说3sum问题求和（和是变量多了一重循

环）

正常是四重循环，这样做一定会超时的！

这里用的是三重循环，其中第三重循环是用2sum问题实现的！

#include<cstdio>#include<algorithm>#include<iostream>#include<cstring>using namespace std;int a[1005];int main(){    int n,i,j,t,l,r,flag;    while(cin>>n&&n)    {        for(i=0;i<n;i++)        {            cin>>a[i];        }        sort(a,a+n);        flag=0;        for(i=n-1;i>=0;i--)        {            for(j=n-1;j>=0;j--)            {                if(i!=j)                {                    t=a[i]-a[j];                    for(l=0,r=j-1;l<r;)                    {                        if(a[l]+a[r]==t)                        {                            flag=1;                            break;                        }                        else if(a[l]+a[r]>t)                        {                            r--;                        }                        else                        {                            l++;                        }                    }                    if(flag)                    {                        break;                    }                }            }            if(flag)            {                break;            }        }        if(flag)        {            cout<<a[i]<<endl;        }        else        {            cout<<"no solution"<<endl;        }    }}

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