poj--2549--Sumsets（二分查找）

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Sumsets

Time Limit: 1000MS Memory Limit: 65536KB 64bit IO Format: %I64d & %I64u

SubmitStatus

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

/*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 -0x3f3f3fint 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);elseprintf("no solution\n");}return 0;}

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