Midsearch

 1 //查找某一个数key的时间复杂度为O(log2n) 
 2 #include<iostream>
 3 using namespace std;
 4 void midsearch(int key,int a[],int n)
 5 {//二分查找是闭区间内查找 
 6     int l=0;
 7     int r=n-1;
 8     int mid;
 9     while(l<=r){
10         mid=(l+r)/2;
11         if(key==a[mid]){
12             cout<<"找到了"<<endl;
13             break;
14         } 
15         else if(key>a[mid])  l=mid+1;
16         else r=mid-1;
17     }
18     if(l>r) cout<<"没有找到"<<endl;    
19 }
20 int main()
21 {
22     int a[]={1,2,3,4,5,6,7,8,9,10};
23     int key;
24     cin>>key;
25     midsearch(key,a,10);
26     return 0;
27 }