【LeetCode 0024】【链表】交换单链表相邻两个节点

24. Swap Nodes in Pairs

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 1:

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

Example 2:

**Input:** head = []
**Output:** []

Example 3:

**Input:** head = [1]
**Output:** [1]

Constraints:

• The number of nodes in the list is in the range [0, 100].
• 0 <= Node.val <= 100

Idea

使用三个指针迭代整条链表
current/next 表示待交换的2个节点指针
prev 表示比较2个节点的第一个节点的前一个节点

JavaScript Solution

/**
 * 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}
 */
var swapPairs = function(head) {
    let dummyHead = new ListNode(-1,head)
    let prev = dummyHead
    while(prev && prev.next && prev.next.next){
      let current = prev.next
      let next = prev.next.next.next
      prev.next = prev.next.next
      prev.next.next = current
      current.next = next
      prev = current
    }
    return dummyHead.next
};