HDU 2578（二分查找）

686MS

 #include <iostream>
 #include <cstdlib>
 #include <cstdio>
 #include <algorithm>

 using namespace std;

 int a[];

 int n;

 bool bsearch(int key)
 {
           int lo = ,hi = n-,mid = lo+(hi-lo)/;
           while(lo<=hi)
           {
                     if(key==a[mid])
                               return true;
                     else if(key >a[mid])
                     {
                               lo = mid+;
                               mid = lo+(hi-lo)/;

                     }
                     else
                     {
                               hi = mid-;
                               mid =lo+(hi-lo)/;
                     }
           }
           return false;
 }

 int main()
 {
     int t,m,i;
     scanf("%d",&t);
     while (t--)
     {
         scanf("%d%d",&n,&m);
         for(i = ;i<n;i++)
                               scanf("%d",&a[i]);
                     int count = ;

                     sort(a,a+n);

                     for(i = ;i<n;i++)
                     {
                               if(a[i]>m/) break;

                               if(a[i] == a[i-])
                                         continue;

                               if(*a[i]==m)
                                         count++;
                               else if(bsearch(m-a[i]))
                                         count+=;
                     }
                     printf("%d\n",count);
     }
     return ;
 }