---
tags: data_structure_python
---

# First Bad Version <img src="https://img.shields.io/badge/-easy-brightgreen">

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.

**Example:**

Given n = 5, and version = 4 is the first bad version.

call isBadVersion(3) -> false
call isBadVersion(5) -> true
call isBadVersion(4) -> true

Then 4 is the first bad version. 

# Solution

# The isBadVersion API is already defined for you.
# @param version, an integer
# @return a bool
# def isBadVersion(version):

class Solution:
    def firstBadVersion(self, n):
        """
        :type n: int
        :rtype: int
        """
        l = 1
        r = n
        
        while l < r:
            mid = l + (r - l)// 2
            
            if isBadVersion(mid):
                r= mid
            else:
                l = mid+1
        
        return l