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
思路:折半枚举即可;
#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
#include<cmath>
using namespace std;
const int MAX=1000+10;
const int inf=-600000000;
long long int n,a[MAX];
int main(){
while(scanf("%lld",&n)!=EOF&&n){
for(int i=0;i<n;i++)
scanf("%lld",&a[i]);
sort(a,a+n);//应该可以不用考虑
n--;
long long int ans=inf;
for(int i=n;i>=0;i--){
for(int j=n;j>=0;j--){
if(i==j) continue;
long long int sum=a[i]-a[j];
for(int c=0,d=j-1;c<d;){
if(a[c]+a[d]==sum){
ans=a[i];
break;
}else if(a[c]+a[d]>sum){
d--;
}else
c++;
}
if(ans!=inf) break;
}
if(ans!=inf) break;
}
if(ans==inf) printf("no solution\n");
else printf("%d\n",ans);
}
}