algorithm/Week_01/id_121/LeetCode_24_121.java at master · isnotnull/algorithm · GitHub

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/**

* 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 ){

return null;

}

if(head.next == null){

return head;

}

ListNode preNode = head;

ListNode curNode = head.next;

ListNode retNode = curNode;

ListNode newPreNode = null;

while(preNode != null && curNode != null){

removeCurNode(preNode,curNode);

insertBeforeCurNode(newPreNode,preNode,curNode);

preNode = curNode.next.next;

newPreNode = curNode.next;

if(preNode != null){

curNode = preNode.next;

}

return retNode;

}

private void removeCurNode(ListNode preNode,ListNode curNode){

if(preNode != null){

preNode.next = curNode.next;

}

curNode.next = null;

}

private void insertBeforeCurNode(ListNode preNode,ListNode curNode,ListNode node){

node.next = curNode;

if(preNode != null){

preNode.next = node;

}

algorithm/Week_01/id_121/LeetCode_24_121.java at master · isnotnull/algorithm · GitHub

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