leetcode-278：第一个错误的版本

给定 n = 5，并且 version = 4 是第一个错误的版本。
调用 isBadVersion(3) -> false
调用 isBadVersion(5) -> true
调用 isBadVersion(4) -> true
所以，4 是第一个错误的版本。 

# The isBadVersion API is already defined for you.
# @param version, an integer
# @return an integer
# def isBadVersion(version):
class Solution:
    def firstBadVersion(self, n):
        """
        :type n: int
        :rtype: int
        """
        left, right = 1, n
        while left < right:
            mid = (right + left) // 2
            if isBadVersion(mid):
                right = mid
            else:
                left = mid + 1
        return left

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