704.二分查找

class Solution(object):
    def search(self, nums, target):
        n = len(nums)
        left = 0
        right = n - 1
        while left <= right:
            mid = ((right - left) >> 1) + left
            if nums[mid] > target:
                right = mid - 1 
            elif nums[mid] < target:
                left = mid + 1
            elif nums[mid] == target:
                return mid
        return -1 #注意此处，写在while循环外面

此为二分法的第一种写法，target定义在[left,right]里
while left <= right
right = mid - 1