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leetcode--Swap Nodes in Pairs

2024-07-07 03:42:54   228人阅读

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.

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    /**
     * This is a fundamental problem.<br>
     *
     * @param head --The head node of the input linked list
     * @return head of the rotated linked list
     * @author Averill Zheng
     * @version 2014-06-03
     * @since JDK 1.7
     */
    public ListNode swapPairs(ListNode head) {
        ListNode newHead = head;
        if(head != null && head.next != null){
            ListNode currentNode = head;
            ListNode nextNode = currentNode.next;
            newHead = nextNode;
            currentNode.next = nextNode.next;
            nextNode.next = currentNode;
            ListNode previous = currentNode;
            currentNode = currentNode.next;
            while(currentNode != null && currentNode.next != null){
                nextNode = currentNode.next;
                currentNode.next = nextNode.next;
                nextNode.next = currentNode;
                previous.next = nextNode;
                previous = currentNode;
                currentNode = currentNode.next;
            }
        }
        return newHead;
    }
}

　　


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