链表排序--奇偶链表排序

最新推荐文章于 2025-01-27 22:07:19 发布

weixin_38507238

最新推荐文章于 2025-01-27 22:07:19 发布

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本文链接：https://blog.youkuaiyun.com/weixin_38507238/article/details/103107901

本文介绍了一种链表排序算法，该算法首先将链表按奇偶位拆分为两个子链表，接着反转偶数位链表，最后将两个有序链表合并为一个完全升序的链表。通过实例演示了算法的具体实现过程。

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题目描述：一个链表，奇数位升序偶数位降序，让链表变成升序的。比如：1 8 3 6 5 4 7 2 9，最后输出1 2 3 4 5 6 7 8 9。
分析：
这道题可以分成三步：
首先根据奇数位和偶数位拆分成两个链表。
然后对偶数链表进行反转。
最后将两个有序链表进行合并。

package com.Link;
public class 奇偶链表排序 {
	public static void main(String[] args) {		
		ListNode head = new ListNode(1);		
		ListNode node2 = new ListNode(8);
		ListNode node3 = new ListNode(3);
		ListNode node4 = new ListNode(6);
		ListNode node5 = new ListNode(5);
		ListNode node6 = new ListNode(4);
		ListNode node7 = new ListNode(7);
		ListNode node8 = new ListNode(2);
		ListNode node9 = new ListNode(9);
		head.next = node2;
		node2.next = node3;
		node3.next = node4;
		node4.next = node5;
		node5.next = node6;
		node6.next = node7;
		node7.next = node8;
		node8.next = node9;
		//printList(head);
		ListNode[] heads = splitList(head);
		//printList(heads[0]);
		//printList(heads[1]);
		ListNode reverseHead =reverseList(heads[1]);
		//printList(reverseHead);
		ListNode mergeHead =mergeLists(heads[0], reverseHead);
		printList(mergeHead);
	}
	// 按照奇偶位拆分成两个链表
	private static  ListNode[] splitList(ListNode head) {
		ListNode head1 = null;
		ListNode head2 = null;
		ListNode cur1 = null;
		ListNode cur2 = null;
		int count = 1;
		while (head != null) {
			if (count % 2 == 1) {
				if (cur1 != null) {
					cur1.next = head;
					cur1 = cur1.next;
				} else {
					cur1 = head;
					head1 = cur1;
				}
			} else {
				if (cur2 != null) {
					cur2.next = head;
					cur2 = cur2.next;
				} else {
					cur2 = head;
					head2 = cur2;
				}
			}
			head = head.next;
			++count;
		}
		// 跳出循环，要让最后两个末尾元素的下一个都指向null
		cur1.next = null;
		cur2.next = null;
		ListNode[] heads = new ListNode[]{head1, head2};
		return heads;
	}
	// 反转链表
	private static ListNode reverseList(ListNode head) {
		ListNode cur = head;
		ListNode pre = null;
		ListNode next = null;
		while (cur != null) {
			next = cur.next;
			cur.next = pre;
			pre = cur;
			cur = next;
		}
		return pre;
	}
	// 合并两个有序链表
	private static ListNode mergeLists(ListNode head1, ListNode head2) {
		if (head1 == null && head2 == null) return null;		
		if (head1 == null || head2 == null) 
			return head1 == null ? head2 : head1;		
		ListNode first = new ListNode(-1);
		ListNode cur = first;
		while (head1 != null && head2 != null) {
			if (head1.val < head2.val) {
				cur.next = head1;
				head1 = head1.next;
			} else {
				cur.next = head2;
				head2 = head2.next;
			}
			cur = cur.next;
		}
		cur.next = head1 != null ? head1 : head2;
		return first.next;
	}

	// 初始化链表
	

	// 打印链表
	private static void printList(ListNode head) {
		if (head == null) return;
		ListNode cur = head;
		while (cur.next != null) {
			System.out.print(cur.val + "\t");
			cur = cur.next;
		}
		System.out.println(cur.val);
	}

	public static class ListNode {
		 int val;
		 ListNode next;
		 ListNode(int val) {
			this.val = val;
		}
	}
}