LeetCode-24. Swap Nodes in Pairs

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问题描述

Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list’s nodes (i.e., only nodes themselves may be changed.)

Example :

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Input: head = [1,2,3,4]
Output: [2,1,4,3]

解答

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/*
 * @Description: 24. Swap Nodes in Pairs
 * @Author: libk
 * @Github: https://github.com/libk
 */
/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
const swapPairs = function(head) {
  if (head === null || head.next === null) {
    return head
  }
  let dummy = new ListNode()
  dummy.next = head
  let pre = dummy
  let cur = head
  while (cur !== null && cur.next !== null) {
    let temp = cur.next
    cur.next = temp.next
    temp.next = pre.next
    pre.next = temp
    pre = cur
    cur = cur.next
  }
  return dummy.next
}