Difficulty: Medium
Given a linked list, swap every two adjacent nodes and return its head.
You may not modify the values in the list's nodes, only nodes itself may be changed.
Example:
Given 1->2->3->4, you should return the list as 2->1->4->3.
Language: Java
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode swapPairs(ListNode head) {
if (head == null || head.next == null) {
return head;
}
ListNode temp = head.next;
head.next = temp.next;
temp.next = head;
head = temp;
ListNode frontNode = head.next.next;
ListNode backNode = head.next;
while (frontNode != null && frontNode.next != null) {
temp = frontNode.next;
backNode.next = temp;
frontNode.next = temp.next;
temp.next = frontNode;
backNode = backNode.next;
frontNode = frontNode.next;
backNode = backNode.next;
}
return head;
}
}