LeetCode 278. First Bad Version

原创于 2016-04-26 11:41:53 发布 · 231 阅读

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本文介绍了一种使用二分查找算法来高效确定首次出现故障的产品版本的方法。在一个有序的产品版本序列中，一旦某个版本开始出现故障，之后的所有版本都将受到影响。通过调用一个名为isBadVersion的API，该算法能最小化检查次数，快速定位首个故障版本。

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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.

this is a variation of binary search.

convert the question into this one would be easier: [0, 0, 0, 1, 1] which returns the index of first 1.

    int firstBadVersion(int n) {
        int left = 1, right = n;
        while(left < right) {
            int mid = left + (right - left) / 2;
            if(isBadVersion(mid) == 0) left = mid + 1;
            else right = mid;
        }
        if(isBadVersion(left)) return left;
        return -1;
    }