LeetCode | Swap Nodes in Pairs

题目

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.

分析

按部就班，用个哨兵简化代码。

代码

public class SwapNodesInPairs {
	public ListNode swapPairs(ListNode head) {
		ListNode dummy = new ListNode(0);
		dummy.next = head;

		ListNode pPre = dummy;
		ListNode p = head;
		while (p != null && p.next != null) {
			// swap
			pPre.next = p.next;
			p.next = p.next.next;
			pPre.next.next = p;

			// move
			pPre = p;
			p = pPre.next;
		}

		return dummy.next;
	}
}