HDU 2578（二分查找）

686MS

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

using namespace std;

int a[100010];

int n;

bool bsearch(int key)
{
          int lo = 0,hi = n-1,mid = lo+(hi-lo)/2;
          while(lo<=hi)
          {
                    if(key==a[mid])
                              return true;
                    else if(key >a[mid])
                    {
                              lo = mid+1;
                              mid = lo+(hi-lo)/2;

                    }
                    else
                    {
                              hi = mid-1;
                              mid =lo+(hi-lo)/2;
                    }
          }
          return false;
}

int main()
{
    int t,m,i;
    scanf("%d",&t);
    while (t--)
    {
        scanf("%d%d",&n,&m);
        for(i = 0;i<n;i++)
                              scanf("%d",&a[i]);
                    int count = 0;

                    sort(a,a+n);

                    for(i = 0;i<n;i++)
                    {
                              if(a[i]>m/2) break;

                              if(a[i] == a[i-1])
                                        continue;

                              if(2*a[i]==m)
                                        count++;
                              else if(bsearch(m-a[i]))
                                        count+=2;
                    }
                    printf("%d
",count);
    }
    return 0;
}