二分查找算法程序如下：

语言环境：Python 3.5

class Solution:
    def binarysearch(self, nums, target):
        """ :type nums:list :type target: int :rtype:int """
        left = 0
        right = len(nums)-1
        while left <= right:
            middle = (left+right)//2
            if nums[middle]==target:
                return middle
            elif nums[middle] < target:
                left = middle + 1
            else:
                right = middle - 1

        return -1