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;
}