Leetcode 278 First Bad Version 二分查找（二分下标）

题意：找到第一个出问题的版本

二分查找，注意 mid = l + (r - l + 1) / 2;因为整数会溢出

 // Forward declaration of isBadVersion API.
 bool isBadVersion(int version);

 class Solution {
 public:
     int firstBadVersion(int n) {
         int l = , r = n , ans ;
         while(l <= r){
             int mid = l +  (r - l + ) / ;
             if(!isBadVersion(mid)){
                 l = mid + ;
             }
             else {
                 r = mid - ;
                 ans = mid;
             }
         }
         return ans;
     }
 };