leetcode/top-100-liked/33/33_test.go

package top100liked

import (
	"fmt"
	"testing"
)

// https://leetcode.cn/problems/reverse-nodes-in-k-group/description/?envType=study-plan-v2&envId=top-100-liked

type ListNode struct {
	Val  int
	Next *ListNode
}

// 模拟冒泡，超时了
// func sortList(head *ListNode) *ListNode {
// 	if head == nil {
// 		return nil
// 	}
// 	if head.Next == nil {
// 		return head
// 	}
// 	dummy := &ListNode{Next: head}
// 	count := 0
// 	l := 0
// 	var p1, p2, p3 *ListNode
// 	for i := 0; l == 0 || l != i; i++ {
// 		p1, p2, p3 = dummy, dummy.Next, dummy.Next.Next
// 		for p3 != nil {
// 			if p2.Val > p3.Val {
// 				p1.Next = p3
// 				p2.Next = p3.Next
// 				p3.Next = p2
// 				p2, p3 = p3, p2
// 			}
// 			if l == 0 {
// 				// 首次遍历
// 				count++
// 			} else if count >= l-i {
// 				break
// 			}
// 			p1 = p1.Next
// 			p2 = p2.Next
// 			p3 = p3.Next
// 		}
// 		if l == 0 {
// 			l = count
// 		}
// 		count = 0
// 	}
// 	return dummy.Next
// }

// 归并排序
func f(head, tail *ListNode) *ListNode {
	if head == nil || tail == nil || head == tail {
		return head
	}
	if head.Next == tail {
		if head.Val > tail.Val {
			tail.Next = head
			head.Next = nil
			return tail
		} else {
			return head
		}
	}
	// 找中点
	slow, fast := head, head
	for fast != nil && fast.Next != nil {
		slow = slow.Next
		fast = fast.Next.Next
	}

	// slow 是中点
	postSlow := slow.Next
	slow.Next = nil
	tail.Next = nil
	left := f(head, slow)
	right := f(postSlow, tail)
	newHead := &ListNode{}
	p1, p2, p3 := left, right, newHead
	for p1 != nil || p2 != nil {
		if p1 == nil || (p2 != nil && p1.Val > p2.Val) {
			p3.Next = p2
			p3 = p3.Next
			p2 = p2.Next
		} else if p2 == nil || p1.Val <= p2.Val {
			p3.Next = p1
			p3 = p3.Next
			p1 = p1.Next
		}
	}
	return newHead.Next
}

func sortList(head *ListNode) *ListNode {
	if head == nil {
		return nil
	}
	if head.Next == nil {
		return head
	}
	cur := head
	for cur.Next != nil {
		cur = cur.Next
	}
	return f(head, cur)
}

func Test1(t *testing.T) {
	input := &ListNode{
		Val: 4,
		Next: &ListNode{
			Val: 2,
			Next: &ListNode{
				Val: 1,
				Next: &ListNode{
					Val:  3,
					Next: nil,
				},
			},
		},
	}
	output := sortList(input)
	for output != nil {
		fmt.Print(output.Val, " ")
		output = output.Next
	}
}

func Test2(t *testing.T) {
	input := &ListNode{
		Val: -1,
		Next: &ListNode{
			Val: 5,
			Next: &ListNode{
				Val: 3,
				Next: &ListNode{
					Val: 4,
					Next: &ListNode{
						Val:  0,
						Next: nil,
					},
				},
			},
		},
	}
	output := sortList(input)
	for output != nil {
		fmt.Print(output.Val, " ")
		output = output.Next
	}
	fmt.Println()
}