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leetcode 024

admin 11月 13, 2020 0

Swap Nodes in Pairs
Method
Java Solution

Swap Nodes in Pairs

Given a linked list, swap every two adjacent nodes and return its head.

For example,
Given1->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.

Method

Basic node.

Java Solution

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode swapPairs(ListNode head) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode pre = dummy;
        while (pre.next!=null && pre.next.next!=null){
            ListNode flag = pre.next.next;
            pre.next.next = flag.next;
            flag.next = pre.next;
            pre.next = flag;
            pre = flag.next;  
        }
        return dummy.next;
    }
}