Leetcode打卡 278. 第一个错误的版本

解题核心：二分法降低计算复杂度

流程图（代表整体思路）

// The API isBadVersion is defined for you.
// bool isBadVersion(int version);

class Solution {
public:
   
    int firstBadVersion(int n) {
        int left=1,right=n;
        if(isBadVersion(1))
           return 1;
        int mid = left + (right - left) / 2;
        while(mid!=left){//有规律总结而得终止条件
            if(isBadVersion(mid))
               right=mid;
            else
               left=mid;
            mid = left + (right - left) / 2;
        }
        return mid+1;//效果等同于   return right 
    }
};