feat: 143. Reorder List : 反转链表 + 双指针

Author: upupming

leetcode/残酷刷题/143. Reorder List.js

@@ -0,0 +1,51 @@
+/**
+ * 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 {void} Do not return anything, modify head in-place instead.
+ */
+const reorderList = function (head) {
+  let sz = 0; let a = head
+  while (a) sz++, a = a.next
+
+  a = head
+  for (let i = 0; i < Math.floor((sz - 1) / 2); i++) {
+    a = a.next
+  }
+  let head2 = a.next
+  a.next = null
+  head2 = reverse(head2)
+
+  const dummy = new ListNode()
+  let p = head; let q = head2; let cur = dummy
+  while (p || q) {
+    if (p) {
+      cur.next = p
+      p = p.next
+      cur = cur.next
+    }
+    if (q) {
+      cur.next = q
+      q = q.next
+      cur = cur.next
+    }
+  }
+  return dummy.next
+}
+
+function reverse (head) {
+  if (!head) return null
+  let a = head; let b = a.next
+  head.next = null
+  while (b) {
+    const c = b.next
+    b.next = a
+    a = b, b = c
+  }
+  return a
+}

leetcode/残酷刷题/README.md

@@ -173,6 +173,7 @@
 - 92. Reverse Linked List II
 - 25. Reverse Nodes in k-Group
 - 2074. Reverse Nodes in Even Length Groups
+- 143. Reorder List
 
 ## Links