Swap Nodes in Pairs

最新推荐文章于 2019-05-11 21:02:45 发布

原创最新推荐文章于 2019-05-11 21:02:45 发布 · 160 阅读

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#LinkedList #Javascript #Interview #Easy #Leetcode

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本文介绍了一种算法，该算法能在常数空间内交换给定链表中的每两个相邻节点，通过改变节点指针而非节点值实现。例如将1->2->3->4变换为2->1->4->3。此算法适用于链表操作和数据结构优化。

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.

Tags

LinkedList

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------

var prev, next;

=>prev=>node=>node.next=>next

Find a general node, we can figure out the rule if swapping between two different nodes:

var next = node.next.next;

prev.next = node.next;

node.next.next = node;

prev = node;

After the changes above, we can get two nodes swapped.

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var swapPairs = function (head) {
    if (head === null || head.next === null) {
        return head;
    }

    var node = head;
    var newNode = new ListNode(-1);
    var prev = newNode;
    prev.next = head;

    while (node && node.next) {
        var next = node.next.next;
        prev.next = node.next;
        node.next.next = node;
        node.next = next;

        prev = node;
        node = prev.next;
    }

    return newNode.next;
};