p278

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LeetCode p278 First Bad Version 题解

1.题目：

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.

题意：

输入n有n个版本 isBadVersion(version) 可以查到版本是否是坏的
找到第一个坏的版本

2.解题思路:

二分
注意防止溢出

3.代码

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/* The isBadVersion API is defined in the parent class VersionControl.
      boolean isBadVersion(int version); */

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        if (isBadVersion(1) == true) return 1;
        int left = 1, right = n;
		int mid = left / 2 + right / 2;  //防止溢出
		while (left < right + 1) {
			if (isBadVersion(mid) == false && isBadVersion(mid + 1) == true) {
				return mid + 1;
			}
			if (isBadVersion(mid)) {
				right = mid ;
			} else {
				left = mid + 1;
			}
			mid = left / 2 + right / 2;

		}
		return right;
    }
}

4.一些总结：