/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var oddEvenList = function(head) {
    const preOdd = new ListNode(-1);
    const preEven = new ListNode(-1);
    let currOdd = preOdd;

    let currEven = preEven;

    let curr = head;
    let isOdd = true;
    while(curr){
        if(isOdd){
            currOdd.next = curr
            currOdd = currOdd.next
        } else {
            currEven.next = curr
            currEven = currEven.next
        }
        isOdd = !isOdd
        curr = curr.next
    }

    currOdd.next = preEven.next;
    return preOdd.next


};