278. 第一个错误的版本

 1 // Forward declaration of isBadVersion API.
 2 bool isBadVersion(int version);
 3 
 4 class Solution 
 5 {
 6 public:
 7     int firstBadVersion(int n) 
 8     {
 9         int l = 1,r = n;
10         while(l < r)
11         {
12             //防止溢出+long long
13             int mid = (long long)l + r >> 1;
14             if(isBadVersion(mid)) r = mid;
15             else l = mid + 1;
16         }
17         return l;
18     }
19 };