[LeetCode Sync] Runtime - 15 ms (95.28%), Memory - 39.2 MB (49.46%)

Author: NinePiece2

Solutions/0234-palindrome-linked-list/README.md

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+<p>Given the <code>head</code> of a singly linked list, return <code>true</code><em> if it is a </em><span data-keyword="palindrome-sequence"><em>palindrome</em></span><em> or </em><code>false</code><em> otherwise</em>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2021/03/03/pal1linked-list.jpg" style="width: 422px; height: 62px;" />
+<pre>
+<strong>Input:</strong> head = [1,2,2,1]
+<strong>Output:</strong> true
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2021/03/03/pal2linked-list.jpg" style="width: 182px; height: 62px;" />
+<pre>
+<strong>Input:</strong> head = [1,2]
+<strong>Output:</strong> false
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li>The number of nodes in the list is in the range <code>[1, 10<sup>5</sup>]</code>.</li>
+	<li><code>0 &lt;= Node.val &lt;= 9</code></li>
+</ul>
+
+<p>&nbsp;</p>
+<strong>Follow up:</strong> Could you do it in <code>O(n)</code> time and <code>O(1)</code> space?

Solutions/0234-palindrome-linked-list/solution.py

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+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def isPalindrome(self, head: Optional[ListNode]) -> bool:
+        # slow, fast = head, head.next
+        # while fast and fast.next:
+        #     slow, fast = slow.next, fast.next.next
+        # last, current = None, slow.next
+
+        # while current:
+        #     tmp = current.next
+        #     current.next = last
+        #     last, current = current, tmp
+
+        # while last:
+        #     if last.val != head.val:
+        #         return False
+        #     last, head = last.next, head.next
+        
+        # return True
+
+        dummy = head
+        nums = []
+        while dummy:
+            nums.append(dummy.val)
+            dummy = dummy.next
+        return nums == nums[::-1]