Leetcode palindrome linked list

linked-list.md

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+# Linked list
+
++ [Palindrome Linked List](#palindrome-linked-list)
+
+## Palindrome Linked List
+
+https://leetcode.com/problems/palindrome-linked-list/
+
+```python
+# Definition for singly-linked list.
+# class ListNode(object):
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution(object):
+    def isPalindrome(self, head):
+        """
+        :type head: ListNode
+        :rtype: bool
+        """
+        mid = tail = head
+        while tail and tail.next:
+            mid = mid.next
+            tail = tail.next.next
+
+        if mid is None:
+            return True
+        if mid.next is None:
+            return head.val == mid.val
+
+        mid.next.next, mid.next, tail, mid = mid, None, mid.next.next, mid.next
+        while tail:
+            tail.next, mid, tail = mid, tail, tail.next
+
+        while mid and head.val == mid.val:
+            head, mid = head.next, mid.next
+        return not mid
+
+```