【LeetCode】Sort List

最新推荐文章于 2022-02-24 15:47:33 发布

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最新推荐文章于 2022-02-24 15:47:33 发布

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分类专栏： leetcode 文章标签： leetcode 链表

本文链接：https://blog.youkuaiyun.com/gfgdsg/article/details/41243875

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本文介绍了一种使用假头节点简化链表合并的方法，并通过递归思想实现链表排序。此外，还提供了一种将多个有序链表合并为一个有序链表的算法。

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/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
ListNode *mergeTwoLists(ListNode *l1, ListNode *l2)
{
	if (l1 == NULL)
		return l2;
	if (l2 == NULL)
		return l1;
	ListNode *fakehead = new ListNode(0);
	ListNode *cur;
	cur = fakehead;
	while (l1 && l2)
	{
		if (l1->val < l2->val)
		{
			cur->next = l1;
			cur = l1;
			l1 = l1->next;
		}
		else
		{
			cur->next = l2;
			cur = l2;
			l2 = l2->next;
		}
	}
	if (l1)
	{
		cur->next = l1;
	}
	else if (l2)
	{
		cur->next = l2;
	}
	return fakehead->next;
}
//6.3 Merge k Sorted Lists
ListNode *mergeKLists(vector<ListNode *> &lists)
{
	if (lists.size() == 0)
		return NULL;
	ListNode *tmp = lists[0];
	for (int i = 1; i < lists.size(); i++)
	{
		tmp = mergeTwoLists(tmp, lists[i]);
	}
	return tmp;
}
//6.5 Sort List
ListNode *sortList(ListNode *head)
{
	ListNode *fast, *slow;
	if (head == NULL || head->next==NULL )
		return head;
	fast = head; slow = head;
	while (fast->next != NULL && fast->next->next != NULL)
	{
		fast = fast->next->next;
		slow = slow->next;
	}
	fast = slow;
	slow = slow->next;
	fast->next = NULL;
	ListNode *firstHalf = sortList(head);
	ListNode *lastHalf = sortList(slow);
	return mergeTwoLists(firstHalf, lastHalf);
}
};