ZOJ 1101

#include<stdio.h>//二分搜索技术运用。此题在排序后应用减法从右往左。
#include<stdlib.h>
#include<string.h>

int a[1001],i,j,k,ncases;
int search(int num,int from,int end)
{
    int mid;
    while(from <= end) 
    { 
       mid = (from+end)/2; 
       if(num == a[mid])
            return 1;
       if(num < a[mid])
          end = mid-1;              
       else
           from = mid+1;
    }
    return 0;
}

int cmp(const void *a,const void *b)
{
    return *(int *)a - *(int *)b;
}
             
int main()
{     
   int sum,tmp,flag;   
   
   while(scanf("%d",&ncases)&&ncases)
   { 
      for(i=0; i<ncases; i++)
      {
        scanf("%d",&a[i]);
      } 
      qsort(a,ncases,sizeof(a[0]),cmp);        
      flag = 0;
      for(i=ncases-1; i>=0; i--)
      {
        for(j=ncases-1; j>=0; j--)    
        { 
           if(i == j) continue;      
           tmp = a[i] - a[j];        
           for(k=ncases-1; k>=0; k--)
           { 
             if(i==k || j==k)
                continue;       
             sum = tmp - a[k]; 
             if(sum==a[i] || sum==a[j] || sum==a[k])//防止重复
                 continue;
             if(search(sum,0,ncases-1)) 
             {
                printf("%d\n",a[i]);     
                flag = 1; 
                goto H;
             }                           
           }
          }
        } 
       if( !flag )   
          printf("no solution\n");
     H: if(flag==1)  continue;               
   }
     
   return 0;
}