二分查找（Binary Search）

算法要求：

1. 必须采用顺序存储结构。
2. 必须按关键字大小有序排列。

class Solution:
    def search(self , nums: List[int], target: int) -> int:
        # write code here
        length = len(nums)
        left = 0
        right = length - 1
        while not nums:
       		return -1
       	while nums:
       		mid = (left + right)//2
       		if nums[mid] == target:
       			return mid
       		elif nums[mid] > target:
                right = mid - 1
            elif nums[mid] < target:
                left = mid + 1
		return -1