UVA Closest Sums（二分查找）

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>

int a[10000100];
int b[10001000];
int sum[100100];

int cmp(const void *a,const void *b)
{
    return *(int*)a - *(int*)b;
}

int main()
{
    int n,m;
    int kk = 0;
    while(scanf("%d",&n)!=EOF)
    {
        if(n == 0)
        {
            break;
        }
        for(int i=0; i<n; i++)
        {
            scanf("%d",&a[i]);
        }
        int t = 0;
        for(int i=0; i<n; i++)
        {
            for(int j=i+1; j<n; j++)
            {
                b[t++] = a[i] + a[j];
            }
        }
        qsort(b,t,sizeof(b[0]),cmp);
        
        sum[0] = b[0];
        int p = 1;
        for(int i=1; i<t; i++)
        {
            if(b[i]!=b[i-1])
            {
                sum[p++] = b[i];
            }
        }
        
        int T;
        kk++;
        printf("Case %d:\n",kk);
        scanf("%d",&T);
        while(T--)
        {
            scanf("%d",&m);
            int low = 0;
            int high = p;
            int mid;
            while(low < high)
            {
                mid = (low + high) / 2;
                if(sum[mid] >= m)
                {
                    high = mid;
                }
                else
                {
                    low = mid + 1;
                }
            }
            
            if(fabs(sum[low-1]-m) < fabs(sum[high]-m) && low>0)
            {
                printf("Closest sum to %d is %d.\n",m,sum[low-1]);
            }
            else
            {
                printf("Closest sum to %d is %d.\n",m,sum[high]);
            }

        }
    }
    return 0;
}