Swap Nodes in Pairs
LintCode-451.Swap Nodes in Pairs
Given a linked list, swap every two adjacent nodes and return its head.
Example: Given 1->2->3->4, you should return the list as 2->1->4->3.
Challenge: Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
public class Solution {
/**
* @param head a ListNode
* @return a ListNode
*/
public ListNode swapPairs(ListNode head) {
if (head == null) {
return head;
}
ListNode dummy = new ListNode(-1);
dummy.next = head;
ListNode current = dummy;
while (current.next != null && current.next.next != null) {
ListNode first = current.next;
ListNode second = current.next.next;
first.next = second.next;
second.next = first;
current.next = second;
current = first;
}
return dummy.next;
}
}
Hope this helps,
Michael