234: Palindrome Linked List

LeetCode/linked_list_is_palidrome.py

@@ -0,0 +1,53 @@
+# 234. Palindrome Linked List
+from typing import Optional, List
+
+
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+
+class Solution:
+    def reverse_linked_list(self, head: Optional[ListNode]):
+        pass
+
+    def isPalindrome(self, head: Optional[ListNode]) -> bool:
+        pass
+
+    def is_palindrome_str(self, head: Optional[ListNode]) -> bool:
+        current = head
+        temp_str = ""
+        while current is not None:
+            temp_str += str(current.val)
+            current = current.next
+        return temp_str == temp_str[::-1]
+
+    def insert_from_list(
+        self, head: Optional[ListNode], values: List[int]
+    ) -> Optional[ListNode]:
+        if not values:
+            return None
+
+        head.val = values[0]
+        current = head
+        for value in values[1:]:
+            current.next = ListNode(value)
+            current = current.next
+
+        return head
+
+    def print_linked_list(self, head: Optional[ListNode]):
+        current = head
+        while current is not None:
+            print(current.val, end=" => " if current.next else " \n")
+            current = current.next
+
+
+values = [1, 2, 2, 1]
+head = ListNode()  # Initialize an empty node to serve as the head
+head = Solution().insert_from_list(head=head, values=values)
+Solution().print_linked_list(head=head)
+print(Solution().is_palindrome_str(head=head))
+# Expected Output: 1 -> 2 -> 2 -> 1

recap/palindrome.py

@@ -0,0 +1,21 @@
+# Python3 program to check if a number is Palindrome
+
+# Function to check Palindrome
+def check_palindrome(n):
+    reverse = 0
+    # Copy of the original number so that the original
+    # number remains unchanged while finding the reverse
+    temp = n
+    while temp != 0:
+        reverse = reverse * 10 + temp % 10
+        temp = temp // 10
+    # If reverse is equal to the original number, the
+    # number is palindrome
+    return reverse == n
+
+# Sample Input
+n = -121
+if check_palindrome(n):
+      print("Yes")
+else:
+      print("No")

tests/helpers.py

@@ -0,0 +1,13 @@
+from typing import List
+from LeetCode.is_palindrome_linked_list import ListNode
+
+# Helper function to convert list to linked list (for easy setup in test cases)
+def list_to_linked_list(arr: List[int]):
+    if not arr:
+        return None
+    head = ListNode(arr[0])
+    current = head
+    for value in arr[1:]:
+        current.next = ListNode(value)
+        current = current.next
+    return head

tests/test_leetcode.py

@@ -30,7 +30,9 @@ def test_chalk_replacer(chalk, k, expected):
     assert solution.chalkReplacer(chalk, k) == expected
 
 
-@pytest.mark.parametrize("string_val, repeat, expected", [("leetcode", 2, 6), ("iiii", 1, 36)])
+@pytest.mark.parametrize(
+    "string_val, repeat, expected", [("leetcode", 2, 6), ("iiii", 1, 36)]
+)
 def test_sum_of_digit_1945(string_val, repeat, expected):
     from LeetCode.sum_of_string_digit_1945 import Solution
 
@@ -79,10 +81,18 @@ def test_length_of_longest_substring(s: str, expected: int):
 @pytest.mark.parametrize(
     "s1, s2, expected",
     [
-        ("this apple is sweet", "this apple is sour", ["sweet", "sour"]),  # uncommon words are "sweet" and "sour"
+        (
+            "this apple is sweet",
+            "this apple is sour",
+            ["sweet", "sour"],
+        ),  # uncommon words are "sweet" and "sour"
         ("apple apple", "banana", ["banana"]),  # "banana" is the only uncommon word
         ("apple", "apple", []),  # no uncommon words, both sentences have "apple"
-        ("the quick", "brown fox", ["the", "quick", "brown", "fox"]),  # all words are uncommon
+        (
+            "the quick",
+            "brown fox",
+            ["the", "quick", "brown", "fox"],
+        ),  # all words are uncommon
         ("", "fox", ["fox"]),  # one sentence is empty, uncommon is "fox"
         ("hello world", "", ["hello", "world"]),  # second sentence is empty
         ("a b c", "a b", ["c"]),  # "c" is the only uncommon word
@@ -93,3 +103,30 @@ def test_uncommon_from_sentences(s1: str, s2: str, expected: List[str]):
 
     solution = Solution()
     assert sorted(solution.uncommonFromSentences(s1, s2)) == sorted(expected)
+
+
+def test_is_palindrome(self):
+    from LeetCode.is_palindrome_linked_list import Solution
+    from .helpers import list_to_linked_list
+
+    solution = Solution()
+
+    # Test case 1: Palindrome [1, 2, 2, 1] -> True
+    l1 = list_to_linked_list([1, 2, 2, 1])
+    assert solution.isPalindrome(l1) == True, "Test case 1 failed"
+
+    # Test case 2: Not a palindrome [1, 2] -> False
+    l1 = list_to_linked_list([1, 2])
+    assert solution.isPalindrome(l1) == False, "Test case 2 failed"
+
+    # Test case 3: Single element [1] -> True
+    l1 = list_to_linked_list([1])
+    assert solution.isPalindrome(l1) == True, "Test case 3 failed"
+
+    # Test case 4: Empty list -> True (Assume empty list as a palindrome)
+    l1 = list_to_linked_list([])
+    assert solution.isPalindrome(l1) == True, "Test case 4 failed"
+
+    # Test case 5: Palindrome [1, 0, 1] -> True
+    l1 = list_to_linked_list([1, 0, 1])
+    assert solution.isPalindrome(l1) == True, "Test case 5 failed"