finish 0234

README.md

@@ -34,6 +34,7 @@ since 2021.10.10 / Benben
 - 0144.Binary Tree PreOrder Traversal
 - 0206.Reverse Linked List
 - 0226.Invert Binary Tree
+- 0234.Palindrome Linked List
 - 0509.Fibonacci Number
 - 0543.Diameter of Binary Tree
 - 0704.Binary Search

leetcode-easy/0234-palindrome-linked-list.js

@@ -0,0 +1,71 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @return {boolean}
+ */
+var isPalindrome = function(head) {
+  /**
+   * solution 01
+   */
+
+  // let left = head
+  // let counter = 0
+  //
+  // const traverse = (right) => {
+  //   if (right === null) return true
+  //   let res = traverse(right.next)
+  //
+  //   res = res && (left.val === right.val)
+  //   left = left.next
+  //   return res
+  // }
+  //
+  // return traverse(head)
+
+  /**
+   * solution 02
+   */
+
+  const reverse = (head) => {
+    let cur = head
+    let prev = null
+    let next = null
+    while (cur !== null) {
+      next = cur.next
+      cur.next = prev
+      prev = cur
+      cur = next
+    }
+    return prev
+  }
+
+  let slow = head
+  let fast = head
+
+  while (fast !== null && fast.next !== null) {
+    slow = slow.next
+    fast = fast.next.next
+  }
+
+  if (fast !== null) slow = slow.next
+
+  let left = head
+  let right = reverse(slow)
+
+  while (right !== null) {
+    if (left.val !== right.val) return false
+    left = left.next
+    right = right.next
+  }
+  return true
+};
+
+// 2022/05/08 done.
+// Runtime: 203 ms, faster than 50.96% of JavaScript online submissions for Palindrome Linked List.
+// Memory Usage: 68.7 MB, less than 89.18% of JavaScript online submissions for Palindrome Linked List.