二分查找

# 为了返回找到列表的下标，故而携带两个参数
def binary_search(num, my_list, left, right):
    if left == right:
        return left if my_list[left] == num else f'没找到{num}'
    mid = (right+left) // 2
    mid_num = my_list[mid]
    if num == mid_num:
        return mid
    elif num > mid_num:
        return binary_search(num, my_list, mid+1, right)
    else:
        return binary_search(num, my_list, left, mid-1)


# 二分查找的循环实现
def while_binary_search(num, lis):
    left = 0
    right = len(lis) - 1
    while True:
        if left == right:
            return left if lis[left] == num else f'没找到{num}'
        mid = (left+right) // 2
        mid_num = lis[mid]
        if mid_num == num:
            return mid
        elif mid_num > num:
            right = mid - 1
        else:
            left = mid + 1


if __name__ == '__main__':
    my_list = [0, 1, 5, 7, 10, 11, 15, 18, 19]
    # print(binary_search(10, my_list, 0, len(my_list)-1))
    print(while_binary_search(15, my_list))