278. First Bad Version

最新推荐文章于 2019-10-30 23:01:54 发布

mll1208596630

最新推荐文章于 2019-10-30 23:01:54 发布

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分类专栏： LeetCode

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作为产品经理，你需要找到导致后续版本故障的首个坏版本。利用提供的API isBadVersion(version)，实现一个函数来找出首个故障版本，尽量减少API调用次数。

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You are a product manager and currently leading a team to develop a new product. Unfortunately, the latest version of your product fails the quality check. Since each version is developed based on the previous version, all the versions after a bad version are also bad.

Suppose you have n versions [1, 2, ..., n] and you want to find out the first bad one, which causes all the following ones to be bad.

You are given an API bool isBadVersion(version) which will return whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.

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

class Solution {
public:
    int check(int s,int e)
    {
        if((s==e)&&isBadVersion(e))
            return e;
        int mid=s+(e-s)/2;
        if(isBadVersion(mid))
        {
            if(mid==s)
                return mid;
            else
                check(s,mid);
        }
        else
            check(mid+1,e);
      
    }
    int firstBadVersion(int n) {
        return check(1,n);
    }
};

计算mid时，不能直接将s和e相加，因为可能造成整数值溢出。。。。