python 二分查找

三种类型的二分查找，当查找的元素当中有重复的时候，第一种是返回中间的值，第二种返回的是最左边的值，第三种返回的是最右边的值。

比如在[0,0,0,1,1,1,1,1,2,2]当中查找1，方法1结果是5， 方法二结果是3，方法三结果是7

class Solution:

    def binary_search(self, nums, target):
        start = 0
        end = len(nums) - 1
        while start <= end:
            mid = (start + end) // 2
            if nums[mid] == target:
                return mid
            elif nums[mid] < target:
                start = mid + 1
            else:
                end = mid - 1
        return -1

    def binary_search_left(self, nums, target):
        start = 0
        end = len(nums) - 1
        while start < end:
            mid = (start + end) // 2
            if nums[mid] < target:
                start = mid + 1
            else:
                end = mid  
        if nums[start] == target:
            return start
        else:
            return -1
    def binary_search_right(self, nums, target):
        start = 0
        end = len(nums) - 1
        while start < end:
            mid = (start + end) // 2 + 1     # mid+1
            if nums[mid] > target:
                end = mid - 1
            else:
                start = mid
        if nums[end] == target:
            return end
        else:
            return -1