给你一个链表,两两交换其中相邻的节点,并返回交换后链表的头节点。你必须在不修改节点内部的值的情况下完成本题(即,只能进行节点交换)。
示例 1:
输入:head = [1,2,3,4] 输出:[2,1,4,3]
示例 2:
输入:head = [] 输出:[]
示例 3:
输入:head = [1] 输出:[1]
/**
* @param {ListNode} head
* @return {ListNode}
*/
var swapPairs = function (head) {
let dummy_node = new ListNode(-1, head);
let prev = dummy_node;
let curr = prev.next
let after = curr ? curr.next : null;
while (curr && after) {
curr.next = after.next;
after.next = curr;
prev.next = after;
prev = curr;
curr = curr ? curr.next : null;
after = curr ? curr.next : null;
}
return dummy_node.next;
};