本文概述
给定一个链表。链表按升序和降序排列。有效地对列表进行排序。
例子：
Input List: 10 -> 40 -> 53 -> 30 -> 67 -> 12 -> 89 -> NULL
Output List: 10 -> 12 -> 30 -> 43 -> 53 -> 67 -> 89 -> NULL
Input List: 1 -> 4 -> 3 -> 2 -> 5 -> NULL
Output List: 1 -> 2 -> 3 -> 4 -> 5 -> NULL简单的解决方案
方法：基本思想是对链表应用合并排序。
本文讨论了实现：合并排序链表.
复杂度分析：
- 时间复杂度：链表的合并排序需要O(n log n)时间。在合并排序树中, 高度为log n。对每个级别进行排序将花费O(n)时间。因此, 时间复杂度为O(n log n)。
- 辅助空间：O(n log n), 在合并排序树中, 高度为log n。存储每个级别将占用O(n)空间。因此, 空间复杂度为O(n log n)。
高效的解决方案
方法：
- 分开两个列表。
- 以降序反转
- 合并两个列表。
图解：
以下是上述算法的实现。
C ++
//C++ program to sort a linked
//list that is alternatively
//sorted in increasing and decreasing order
#include <bits/stdc++.h>
using namespace std;
//Linked list node
struct Node {
int data;
struct Node* next;
};
Node* mergelist(Node* head1, Node* head2);
void splitList(Node* head, Node** Ahead, Node** Dhead);
void reverselist(Node*& head);
//This is the main function that sorts the
//linked list
void sort(Node** head)
{
//Split the list into lists
Node *Ahead, *Dhead;
splitList(*head, &Ahead, &Dhead);
//Reverse the descending linked list
reverselist(Dhead);
//Merge the two linked lists
*head = mergelist(Ahead, Dhead);
}
//A utility function to create a new node
Node* newNode( int key)
{
Node* temp = new Node;
temp->data = key;
temp->next = NULL;
return temp;
}
//A utility function to reverse a linked list
void reverselist(Node*& head)
{
Node *prev = NULL, *curr = head, *next;
while (curr) {
next = curr->next;
curr->next = prev;
prev = curr;
curr = next;
}
head = prev;
}
//A utility function to print a linked list
void printlist(Node* head)
{
while (head != NULL) {
cout <<head->data <<" " ;
head = head->next;
}
cout <<endl;
}
//A utility function to merge two sorted linked lists
Node* mergelist(Node* head1, Node* head2)
{
//Base cases
if (!head1)
return head2;
if (!head2)
return head1;
Node* temp = NULL;
if (head1->data <head2->data) {
temp = head1;
head1->next = mergelist(head1->next, head2);
}
else {
temp = head2;
head2->next = mergelist(head1, head2->next);
}
return temp;
}
//This function alternatively splits
//a linked list with head as head into two:
//For example, 10->20->30->15->40->7 \
//is splitted into 10->30->40
//and 20->15->7
//"Ahead" is reference to head of ascending linked list
//"Dhead" is reference to head of descending linked list
void splitList(Node* head, Node** Ahead, Node** Dhead)
{
//Create two dummy nodes to initialize
//heads of two linked list
*Ahead = newNode(0);
*Dhead = newNode(0);
Node* ascn = *Ahead;
Node* dscn = *Dhead;
Node* curr = head;
//Link alternate nodes
while (curr) {
//Link alternate nodes of ascending linked list
ascn->next = curr;
ascn = ascn->next;
curr = curr->next;
//Link alternate nodes of descending linked list
if (curr) {
dscn->next = curr;
dscn = dscn->next;
curr = curr->next;
}
}
ascn->next = NULL;
dscn->next = NULL;
*Ahead = (*Ahead)->next;
*Dhead = (*Dhead)->next;
}
//Driver program to test above function
int main()
{
Node* head = newNode(10);
head->next = newNode(40);
head->next->next = newNode(53);
head->next->next->next = newNode(30);
head->next->next->next->next = newNode(67);
head->next->next->next->next->next = newNode(12);
head->next->next->next->next->next->next = newNode(89);
cout <<"Given Linked List is " <<endl;
printlist(head);
sort(&head);
cout <<"Sorted Linked List is " <<endl;
printlist(head);
return 0;
}Java
//Java program to sort a
//linked list that is alternatively
//sorted in increasing and decreasing order
class LinkedList {
Node head; //head of list
/* Linked list Node*/
class Node {
int data;
Node next;
Node( int d)
{
data = d;
next = null ;
}
}
Node newNode( int key)
{
return new Node(key);
}
/* This is the main function that sorts
the linked list.*/
void sort()
{
/* Create 2 dummy nodes and initialise as
heads of linked lists */
Node Ahead = new Node( 0 ), Dhead = new Node( 0 );
//Split the list into lists
splitList(Ahead, Dhead);
Ahead = Ahead.next;
Dhead = Dhead.next;
//reverse the descending list
Dhead = reverseList(Dhead);
//merge the 2 linked lists
head = mergeList(Ahead, Dhead);
}
/* Function to reverse the linked list */
Node reverseList(Node Dhead)
{
Node current = Dhead;
Node prev = null ;
Node next;
while (current != null ) {
next = current.next;
current.next = prev;
prev = current;
current = next;
}
Dhead = prev;
return Dhead;
}
/* Function to print linked list */
void printList()
{
Node temp = head;
while (temp != null ) {
System.out.print(temp.data + " " );
temp = temp.next;
}
System.out.println();
}
//A utility function to merge
//two sorted linked lists
Node mergeList(Node head1, Node head2)
{
//Base cases
if (head1 == null )
return head2;
if (head2 == null )
return head1;
Node temp = null ;
if (head1.data <head2.data) {
temp = head1;
head1.next = mergeList(head1.next, head2);
}
else {
temp = head2;
head2.next = mergeList(head1, head2.next);
}
return temp;
}
//This function alternatively splits
//a linked list with head as head into two:
//For example, 10->20->30->15->40->7 is
//splitted into 10->30->40
//and 20->15->7
//"Ahead" is reference to head of ascending linked list
//"Dhead" is reference to head of descending linked list
void splitList(Node Ahead, Node Dhead)
{
Node ascn = Ahead;
Node dscn = Dhead;
Node curr = head;
//Link alternate nodes
while (curr != null ) {
//Link alternate nodes in ascending order
ascn.next = curr;
ascn = ascn.next;
curr = curr.next;
if (curr != null ) {
dscn.next = curr;
dscn = dscn.next;
curr = curr.next;
}
}
ascn.next = null ;
dscn.next = null ;
}
/* Driver program to test above functions */
public static void main(String args[])
{
LinkedList llist = new LinkedList();
llist.head = llist.newNode( 10 );
llist.head.next = llist.newNode( 40 );
llist.head.next.next = llist.newNode( 53 );
llist.head.next.next.next = llist.newNode( 30 );
llist.head.next.next.next.next = llist.newNode( 67 );
llist.head.next.next.next.next.next = llist.newNode( 12 );
llist.head.next.next.next.next.next.next = llist.newNode( 89 );
System.out.println( "Given linked list" );
llist.printList();
llist.sort();
System.out.println( "Sorted linked list" );
llist.printList();
}
} /* This code is contributed by Rajat Mishra */python
# Python program to sort a linked list that is alternatively
# sorted in increasing and decreasing order
class LinkedList( object ):
def __init__( self ):
self .head = None
# Linked list Node
class Node( object ):
def __init__( self , d):
self .data = d
self . next = None
def newNode( self , key):
return self .Node(key)
# This is the main function that sorts
# the linked list.
def sort( self ):
# Create 2 dummy nodes and initialise as
# heads of linked lists
Ahead = self .Node( 0 )
Dhead = self .Node( 0 )
# Split the list into lists
self .splitList(Ahead, Dhead)
Ahead = Ahead. next
Dhead = Dhead. next
# reverse the descending list
Dhead = self .reverseList(Dhead)
# merge the 2 linked lists
self .head = self .mergeList(Ahead, Dhead)
# Function to reverse the linked list
def reverseList( self , Dhead):
current = Dhead
prev = None
while current ! = None :
self ._next = current. next
current. next = prev
prev = current
current = self ._next
Dhead = prev
return Dhead
# Function to print linked list
def printList( self ):
temp = self .head
while temp ! = None :
print temp.data, temp = temp. next
print ''
# A utility function to merge two sorted linked lists
def mergeList( self , head1, head2):
# Base cases
if head1 = = None :
return head2
if head2 = = None :
return head1
temp = None
if head1.data <head2.data:
temp = head1
head1. next = self .mergeList(head1. next , head2)
else :
temp = head2
head2. next = self .mergeList(head1, head2. next )
return temp
# This function alternatively splits a linked list with head
# as head into two:
# For example, 10->20->30->15->40->7 is splitted into 10->30->40
# and 20->15->7
# "Ahead" is reference to head of ascending linked list
# "Dhead" is reference to head of descending linked list
def splitList( self , Ahead, Dhead):
ascn = Ahead
dscn = Dhead
curr = self .head
# Link alternate nodes
while curr ! = None :
# Link alternate nodes in ascending order
ascn. next = curr
ascn = ascn. next
curr = curr. next
if curr ! = None :
dscn. next = curr
dscn = dscn. next
curr = curr. next
ascn. next = None
dscn. next = None
# Driver program
llist = LinkedList()
llist.head = llist.newNode( 10 )
llist.head. next = llist.newNode( 40 )
llist.head. next . next = llist.newNode( 53 )
llist.head. next . next . next = llist.newNode( 30 )
llist.head. next . next . next . next = llist.newNode( 67 )
llist.head. next . next . next . next . next = llist.newNode( 12 )
llist.head. next . next . next . next . next . next = llist.newNode( 89 )
print 'Given linked list'
llist.printList()
llist.sort()
print 'Sorted linked list'
llist.printList()
# This code is contributed by BHAVYA JAINC#
//C# program to sort a linked list that is alternatively
//sorted in increasing and decreasing order
using System;
class LinkedList {
Node head; //head of list
/* Linked list Node*/
public class Node {
public int data;
public Node next;
public Node( int d)
{
data = d;
next = null ;
}
}
Node newNode( int key)
{
return new Node(key);
}
/* This is the main function that sorts
the linked list.*/
void sort()
{
/* Create 2 dummy nodes and initialise as
heads of linked lists */
Node Ahead = new Node(0), Dhead = new Node(0);
//Split the list into lists
splitList(Ahead, Dhead);
Ahead = Ahead.next;
Dhead = Dhead.next;
//reverse the descending list
Dhead = reverseList(Dhead);
//merge the 2 linked lists
head = mergeList(Ahead, Dhead);
}
/* Function to reverse the linked list */
Node reverseList(Node Dhead)
{
Node current = Dhead;
Node prev = null ;
Node next;
while (current != null ) {
next = current.next;
current.next = prev;
prev = current;
current = next;
}
Dhead = prev;
return Dhead;
}
/* Function to print linked list */
void printList()
{
Node temp = head;
while (temp != null ) {
Console.Write(temp.data + " " );
temp = temp.next;
}
Console.WriteLine();
}
//A utility function to merge two sorted linked lists
Node mergeList(Node head1, Node head2)
{
//Base cases
if (head1 == null )
return head2;
if (head2 == null )
return head1;
Node temp = null ;
if (head1.data <head2.data) {
temp = head1;
head1.next = mergeList(head1.next, head2);
}
else {
temp = head2;
head2.next = mergeList(head1, head2.next);
}
return temp;
}
//This function alternatively splits a linked list with head
//as head into two:
//For example, 10->20->30->15->40->7 is splitted into 10->30->40
//and 20->15->7
//"Ahead" is reference to head of ascending linked list
//"Dhead" is reference to head of descending linked list
void splitList(Node Ahead, Node Dhead)
{
Node ascn = Ahead;
Node dscn = Dhead;
Node curr = head;
//Link alternate nodes
while (curr != null ) {
//Link alternate nodes in ascending order
ascn.next = curr;
ascn = ascn.next;
curr = curr.next;
if (curr != null ) {
dscn.next = curr;
dscn = dscn.next;
curr = curr.next;
}
}
ascn.next = null ;
dscn.next = null ;
}
/* Driver code */
public static void Main(String[] args)
{
LinkedList llist = new LinkedList();
llist.head = llist.newNode(10);
llist.head.next = llist.newNode(40);
llist.head.next.next = llist.newNode(53);
llist.head.next.next.next = llist.newNode(30);
llist.head.next.next.next.next = llist.newNode(67);
llist.head.next.next.next.next.next = llist.newNode(12);
llist.head.next.next.next.next.next.next = llist.newNode(89);
Console.WriteLine( "Given linked list" );
llist.printList();
llist.sort();
Console.WriteLine( "Sorted linked list" );
llist.printList();
}
}
/* This code is contributed by Arnab Kundu */输出如下：
Given Linked List is
10 40 53 30 67 12 89
Sorted Linked List is
10 12 30 40 53 67 89复杂度分析：
- 时间复杂度：O(n)。
需要遍历以分隔列表并将其反转。排序列表的合并需要O(n)时间。 - 辅助空间：O(1)。
不需要额外的空间。
感谢Gaurav Ahirwar提出了这种方法。
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来源：
https://www.srcmini02.com/68817.html
