Python实现二分查找模板

• 遇到数组的时候：
  1.排序or not
  2.数组中有无重复
  3.有无负数

模板代码实现：

def binarysearch(alist, item):
    if len(alist) == 0:  #判断数组是否为空
        return -1
    
    left, right = 0, len(alist) - 1
    while left + 1 < right:
        mid = left + (right - left) // 2
        if alist[mid] == item:
            right = mid
        elif alist[mid] < item:
            left = mid
        elif alist[mid] > item:
            right = mid
    
    if alist[left] == item: 
        return left
    if alist[right] == item:
        return right
    
    return -1