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palindrome-linked-list.py
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palindrome-linked-list.py
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# Definition for singly-linked list.
class ListNode(object):
def __init__(self, x):
self.val = x
self.next = None
# I think I should implement the stack solution here as well , using [::-1] *might* be cheating
# its a construct that is not available in other languages , so ..
class Solution_1(object):
def isPalindrome(self, head):
"""
:type head: ListNode
:rtype: bool
"""
result = []
current = head
if head == None :
return True
else:
while current:
result.append(str(current.val))
current = current.next
return result == result[::-1]
# A simple solution is to use a stack of list nodes. This mainly involves three steps.
# 1) Traverse the given list from head to tail and push every visited node to stack.
# 2) Traverse the list again. For every visited node, pop a node from stack and compare data of popped node with currently visited node.
# 3) If all nodes matched, then return true, else false.
import unittest
class Solution(object):
def isPalindrome(self, head):
"""
:type head: ListNode
:rtype: bool
"""
self.head = head
current = self.head
my_stack = []
if self.head is None:
return True
elif self.head.next is None:
return True
else:
while current.next:
my_stack.append(current.val)
current = current.next
my_stack.append(current.val)
#print my_stack
current = self.head
# print current.val
while current.next:
if current.val == my_stack.pop():
current = current.next
else:
return False
return True
class TestPalindromeLinkedList(unittest.TestCase):
my_solution = Solution()
def test_not_a_palindrome(self):
A,B,C,D,E = ListNode("A"),ListNode("B"),ListNode("C"),ListNode("D"),ListNode("E")
A.next = B
B.next = C
C.next = D
D.next = E
self.assertFalse(self.my_solution.isPalindrome(A))
def test_is_a_palindrome(self):
A,B,C,D,E = ListNode("R"),ListNode("A"),ListNode("D"),ListNode("A"),ListNode("R")
A.next = B
B.next = C
C.next = D
D.next = E
self.assertTrue(self.my_solution.isPalindrome(A))
def test_empty_list(self):
X = ListNode("")
self.assertTrue(self.my_solution.isPalindrome(X))
def test_list_of_length_one(self):
A = ListNode("A")
self.assertTrue(self.my_solution.isPalindrome(A))
if __name__ == "__main__":
unittest.main()