二分法     掐头结尾取中间     查找效率非常的高

# 二分法查找主要的作用就是查找元素# lst = [1,3,5,7,12,36,68,79]     # 数据集 百万级数据# nl = int(input("请输入你要查找的数字:"))# left = 0# right = len(lst)-1# while left <= right:#     mid = (left+right)//2#     if nl > lst[mid]:#         left = mid + 1#     elif nl < lst[mid]:#         right = mid - 1#     else:#         print("存在")#         break# else:#     print("不存在")# 递归# def func(n, lst, left, right):#     mid = (left+right) // 2#     if left <= right:#         if n > lst[mid]:#             left = mid + 1#             return func(n, lst, left, right)#         elif n < lst[mid]:#             right = mid - 1#             return func(n, lst, left, right)#         else:#             print("存在")#             return mid#     else:#         print("不存在")#         return -1# n = int(input("请输入你要查找的数:"))# lst = [1,3,5,7,12,36,68,79]# func(n, lst, 0, len(lst)-1)