二分模板（适用于大部分的二分类题目）

• 下面的模板是在保证搜寻目标肯定在数组中的情况下进行的，可以看出start + 1 < end这行使得二分绝对不会出现左右指针越界或者TLE的情况，最后添加一个在start和end对应的值上的判断在跳出循环后仍可以保证找到元素

list = xxxx                               # 一个长度为n的数组
target = xxxx                             # 搜寻目标
n = len(list)

start, end = 0, n - 1

while start + 1 < end:
    mid = start + (end - start) / 2
    if list[mid] == target:
        return mid
    elif list[mid] < target:
        start = mid
    else:
        end = mid

if list[start] == target:
    return start
return end

Guess Number

这道题就是用纯二分法做即可，唯一需要注意的是这里的guess API返回的那个高或低的标准不是根据猜数字者的视角而是给予正确答案的视角来看的

# The guess API is already defined for you.
# @param num, your guess
# @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
# def guess(num):

class Solution(object):
    def guessNumber(self, n):
        """
        :type n: int
        :rtype: int
        """
        start, end = 0, n - 1
        while start + 1 < end:
            mid = start + (end - start) / 2
            value = guess(mid)
            if value == 1:
                end = mid
            elif value == -1:
                start = mid
            else:
                return mid

        if guess(start) == 0:
            return start
        return end