“ 五月，总结模板的日子.”Day 1  ——  First Bad Version首个坏“蛋”问题描述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 nversions [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 versionis 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) -> falsecall isBadVersion(5) -> truecall isBadVersion(4) -> trueThen 4 is the first bad version. 

解题思路

【典型二分法】

• 没啥好说的，典型二分法~

# 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        """        hi = n        lo = 1        while lo <= hi:            crr = (hi + lo) // 2            if isBadVersion(crr):                hi = crr - 1             else:                lo = crr + 1        return lo

时间复杂度O(logn)，空间复杂度O(1)。

【二分查找有序list】

• 典型二分查找模板，很多题目都可由其变换而来~

def binary_search(list,item):    low = 0    high = len(list) - 1    while low <= high:        mid = int((low + high) / 2)        guess = list[mid]        if guess == item:            return mid        if guess > item:            high = mid - 1        else:            low = mid + 1 my_list = [0,1,3,6,9]print(binary_search(my_list,3))