#!/usr/bin/env python class Node(object):
def __init__(self,elem,next_=None):
self.elem = elem
self.next = next_ class Simple_List(object):
def __init__(self):
self.head = None def is_empty(self):
return self.head == None def prepend(self,elem):
self.head = Node(elem, self.head) def prepop(self):
if self.is_empty():
raise ValueError("list is empty")
e = self.head.elem
self.head = self.head.next
return e def find_the_key(sl,key):
if key < 0:
raise ValueError("key must >= 0")
i,j = sl.head,sl.head
while key:
j = j.next
if j is None:
raise ValueError("key must < list's length")
key -= 1
while j.next:
i,j = i.next,j.next
return i.elem if __name__=="__main__":
sl = Simple_List()
for i in range(5,-1,-1):
sl.prepend(i)
print(find_the_key(sl,0))