278. 第一个错误的版本

# The isBadVersion API is already defined for you.
# def isBadVersion(version: int) -> bool:

class Solution:
    def firstBadVersion(self, n: int) -> int:
        left = 1
        right = n 
        while left <= right:
            half = left + (right-left)//2
            if isBadVersion(half)==False:
                left = half+1
            else:
                right = half-1
        return left