Problem C - Sumsets
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
Output for Sample Input
12no solution
a，b，c，d互异，开始直接排完序三重循环+二分wrong到死，忽略了个问题不该每次穷举a+b+c，这样无法保证每次都是最大的，穷举d，a，b，再二分查c终于水过了
#include<stdio.h>#include<algorithm>#include<string.h>using namespace std;int a[1010],i,j,k,ans,f,n;int comp(int x,int y){return x>y;};int find(int key,int l,int r){int mid=(r+l)/2; if (l>r) return 0; if (key==a[mid]) {if ((mid!=i)&&(mid!=j)&&(mid!=k)) f=1; return 0; } else if (key<a[mid]) find(key,mid+1,r); else find(key,l,mid-1);};int main(){while (scanf("%d",&n),n) { for (i=0;i<n;i++) scanf("%d",&a[i]); sort(a,a+n,comp); f=0; for (i=0;i<n;i++) for (j=0;j<n-1;j++) for (k=j+1;k<n;k++) {ans=a[i]; if ((i!=j)&&(i!=k)) find(a[i]-a[j]-a[k],0,n-1); if (f) goto there; } there:; if (f) printf("%d\n",ans); else printf("no solution\n"); } return 0;}
