package src.leetcode;

import src.common.node.ListNode;

/**

* 两两交换链表中的节点

*/

class Solution1 {

public static void main(String[] args) {

ListNode head = ListNode.genNextNode(new int[]{1,2,3,4});

ListNode listNode = new Solution1().swapPairsDG_Reverse(head);

System.out.println(listNode);

}

public ListNode swapPairsDG_Reverse(ListNode head) {

if(head == null || head.next == null){

return head;

}

ListNode next = head.next;

head.next = swapPairsDG_Reverse(next.next);

next.next = head;

//返回链表头结点

return next;

}

public ListNode swapPairsDG_Order(ListNode head) {

if (head == null || head.next ==null ) {

return null;

}

ListNode nextNode = head.next.next;

ListNode next = head.next;

next.next = head;

head.next = swapPairsDG_Order(nextNode);

//返回链表头结点

return next;

}

//遍历 不懂

public ListNode swapPairs(ListNode head) {

ListNode pre = ListNode.genNextNode(new int[]{0});

pre.next = head;

ListNode temp = pre;

while(temp.next != null && temp.next.next != null) {

ListNode start = temp.next;

ListNode end = temp.next.next;

temp.next = end;

start.next = end.next;

end.next = start;

temp = start;

}

return pre.next;

}

}