24 Swap Nodes in Pairs – Medium
Problem:
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.
Thoughts:
Very basic iteration of the list.
Solutions:
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode swapPairs(ListNode head) {
ListNode fakeHead = new ListNode(-1);
fakeHead.next = head;
ListNode node = fakeHead;
while (node!=null & node.next != null && node.next.next!= null){
ListNode first = node;
ListNode second = node.next;
ListNode third = node.next.next;
first.next = third;
second.next = third.next;
third.next = second;
node = second;
}
return fakeHead.next;
}
}