[LeetCode][JavaScript]Swap Nodes in Pairs

Swap Nodes in Pairs

Given a linked list, swap every two adjacent nodes and return its head.

For example,
Given 1->2->3->4, you should return the list as 2->1->4->3.

Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.

https://leetcode.com/problems/swap-nodes-in-pairs/

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交换链表中相邻的两个节点，要求O(1)的空间复杂度。

 

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var swapPairs = function(head) {
    var newHead = new ListNode(-1), start = newHead;
    newHead.next = head;
    while(start.next !== null && start.next.next !== null)
        start = reverse(start, start.next, start.next.next);            
    return newHead.next;        
    
    function reverse(h, node1, node2){
        var tail = node2.next;
        h.next = node2;
        node2.next = node1;
        node1.next = tail;
        return node1;
    }
};