odd-even-linked-list.js

// Given a singly linked list, group all odd nodes together followed by the even nodes. Please note here we are talking about the node number and not the value in the nodes.
//
// You should try to do it in place. The program should run in O(1) space complexity and O(nodes) time complexity.
//
//
// Example:
// Given 1->2->3->4->5->NULL,
// return 1->3->5->2->4->NULL.
//
//
// Note:
// The relative order inside both the even and odd groups should remain as it was in the input. 
// The first node is considered odd, the second node even and so on ...
//
//
// Credits:Special thanks to @DjangoUnchained for adding this problem and creating all test cases.


/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var oddEvenList = function(head) {
    if (head === null || head.next === null || head.next.next === null) {
        return head;
    }
    var p_odd = head, p_even = head.next, head_of_even = p_even;
    while(p_even !== null &&  p_even.next !== null ) {
        p_odd.next = p_even.next ;
		p_even.next = p_odd.next.next ;
		
		p_odd = p_odd.next ;
		p_even = p_even.next;
    }
    p_odd.next = head_of_even;
    return head;
};