1 /*
2 入门之二分查找
3 时间复杂度：O(logn)
4 只能查找已排序好的数组
5 通过不断比较中间值，确定keyword在中间值的左边或右边，直到找到或结束
6 */
7 #include<iostream>
8 using namespace std;
9 int a[] = {1,2,3,4,5,6,7,8,9};
10 bool binary_search(int,int,int);
11 int main()
12 {
13 int key;
14 while(1){
15 cout << "keyword:";
16 cin >> key;
17 if(binary_search(key,0,8))
18 cout << "Find success" << endl;
19 else
20 cout << "Find failed" << endl;}
21 }
22 bool binary_search(int k,int l,int r)//循环实现
23 {
24 while(l <= r)
25 {
26 int m = (l + r)/2;
27 if(a[m] == k) return true;
28 else if(a[m] > k) r = m-1;
29 else l = m+1;
30 }
31 return false;
32 }
33 bool binary_search(int k,int l,int r)//递归实现
34 {
35 if(l > r) return false;
36 int m = (l + r)/2;
37 if(a[m] == k) return true;
38 else if(a[m] > k) return binary_search(k,l,m-1);
39 else binary_search(k,m+1,r);
40 }
