Swap Nodes in Pairs
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2022-03-05 08:17:05
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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.
/**
* 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 listNode = new ListNode(0);
listNode.next = head;
ListNode p1 = listNode;
ListNode p2 = head;
while (p2 != null && p2.next != null) {
ListNode p3 = p2.next.next;
p2.next.next = p2;
p1.next = p2.next;
p2.next = p3;
p1 = p2;
p2 = p2.next;
}
return listNode.next;
}
}