LeetCode — Odd Even Linked List

Given the head of a singly linked list, group all the nodes with odd indices together followed by the nodes with even indices, and return the reordered list.

The first node is considered odd, and the second node is even, and so on.

Note that the relative order inside both the even and odd groups should remain as it was in the input.

You must solve the problem in O(1) extra space complexity and O(n) time complexity.

Example 1:

Input: head = [1,2,3,4,5]
Output: [1,3,5,2,4]

Example 2:

Input: head = [2,1,3,5,6,4,7]
Output: [2,3,6,7,1,5,4]

Constraints:

• n == number of nodes in the linked list
• 0 <= n <= 104
• -106 <= Node.val <= 106

Accepted

485,743

Submissions

821,448

Solution:

The idea of this solution is to make use of 2 pointers to sort out both odd and even list nodes, and updating it then connecting with the head of even list node.

Time Complexity: O(n)

Space Complexity: O(1)