二分查找法,定义start和end作为搜索范围,根据start和end来确定index

class Solution:
    def search(self , nums: List[int], target: int) -> int:
        # write code here
        nums_len = len(nums) 
        start = 0
        end = nums_len - 1
        while start <= end:
            index = int((start + end) / 2)
            if nums[index] == target:
                return index
            elif nums[index] < target:
                start = index + 1
            else:
                end = index - 1
        return -1