HDU 2578（二分查找）

686MS
 1 #include <iostream>
 2 #include <cstdlib>
 3 #include <cstdio>
 4 #include <algorithm>
 5 
 6 using namespace std;
 7 
 8 int a[100010];
 9 
10 int n;
11 
12 bool bsearch(int key)
13 {
14           int lo = 0,hi = n-1,mid = lo+(hi-lo)/2;
15           while(lo<=hi)
16           {
17                     if(key==a[mid])
18                               return true;
19                     else if(key >a[mid])
20                     {
21                               lo = mid+1;
22                               mid = lo+(hi-lo)/2;
23 
24                     }
25                     else
26                     {
27                               hi = mid-1;
28                               mid =lo+(hi-lo)/2;
29                     }
30           }
31           return false;
32 }
33 
34 int main()
35 {
36     int t,m,i;
37     scanf("%d",&t);
38     while (t--)
39     {
40         scanf("%d%d",&n,&m);
41         for(i = 0;i<n;i++)
42                               scanf("%d",&a[i]);
43                     int count = 0;
44 
45                     sort(a,a+n);
46 
47                     for(i = 0;i<n;i++)
48                     {
49                               if(a[i]>m/2) break;
50 
51                               if(a[i] == a[i-1])
52                                         continue;
53 
54                               if(2*a[i]==m)
55                                         count++;
56                               else if(bsearch(m-a[i]))
57                                         count+=2;
58                     }
59                     printf("%d
",count);
60     }
61     return 0;
62 }