Easy-题目63：278. First Bad Version

题目原文：
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.
题目大意：
你是一个PM，现在率领一个团队开发一个新的产品。不幸的是，其中一个版本没有通过质量检测。而后面的版本由于是基于前面的版本的，所以都是坏的产品。
假设你有n个版本[1,2,…n],你希望找出第一个坏的版本。
现在有一个API bool isBadVersion(version)会返回这个版本是不是坏的。实现一个函数来找出第一个坏的版本。要求这个api尽可能少调用。
题目分析：
最直观不能再直观的二分查找了。如果还不会写二分查找，只能说你这大学白念了……
源码：（language：cpp）

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

class Solution {
public:
    int firstBadVersion(int n) {
        int low = 1;
        int high = n;
        int ver = 0;
        while (low < high) {
            ver = low + (high - low) / 2;
            if (isBadVersion(ver)) {
                high = ver;
            } else {
                low = ver + 1;
            }
        }
        return low;
    }
};

成绩：
0ms,beats 3.21%,众数0ms，96.79%。
cmershen的碎碎念：
像二分查找，包括后面的二叉树遍历，图的dfs，bfs，拓扑排序等最最最基础的问题，反而应当予以高度重视，做到倒背如流，切不可因为简单就不去强化练习。