算法设计：如何从已排序的链表中删除重复项？

2021年3月19日18:24:48 发表评论 670 次浏览

本文概述

编写一个函数, 该函数采用以非降序排列的列表, 并从列表中删除所有重复的节点。该列表仅应遍历一次。

例如, 如果链接列表是11-> 11-> 11-> 21-> 43-> 43-> 60, 则removeDuplicates()会将列表转换为11-> 21-> 43-> 60。

推荐：请在"

实践

首先, 在继续解决方案之前。

算法：

从头(或起始)节点遍历列表。遍历时, 将每个节点与其下一个节点进行比较。如果下一个节点的数据与当前节点相同, 则删除下一个节点。在删除节点之前, 我们需要存储该节点的下一个指针

实现

除了removeDuplicates()以外的函数仅用于创建链接的链表并测试removeDuplicates()。

C ++

/* C++ Program to remove duplicates from a sorted linked list */
#include <bits/stdc++.h>
using namespace std;
 
/* Link list node */
class Node
{
     public :
     int data;
     Node* next;
};
 
/* The function removes duplicates from a sorted list */
void removeDuplicates(Node* head)
{
     /* Pointer to traverse the linked list */
     Node* current = head;
 
     /* Pointer to store the next pointer of a node to be deleted*/
     Node* next_next;
     
     /* do nothing if the list is empty */
     if (current == NULL)
     return ;
 
     /* Traverse the list till last node */
     while (current->next != NULL)
     {
     /* Compare current node with next node */
     if (current->data == current->next->data)
     {
         /* The sequence of steps is important*/       
         next_next = current->next->next;
         free (current->next);
         current->next = next_next;
     }
     else /* This is tricky: only advance if no deletion */
     {
         current = current->next;
     }
     }
}
 
/* UTILITY FUNCTIONS */
/* Function to insert a node at the beginging of the linked list */
void push(Node** head_ref, int new_data)
{
     /* allocate node */
     Node* new_node = new Node();
             
     /* put in the data */
     new_node->data = new_data;
                 
     /* link the old list off the new node */
     new_node->next = (*head_ref);    
         
     /* move the head to point to the new node */
     (*head_ref) = new_node;
}
 
/* Function to print nodes in a given linked list */
void printList(Node *node)
{
     while (node!=NULL)
     {
         cout<< " " <<node->data;
         node = node->next;
     }
}
 
/* Driver program to test above functions*/
int main()
{
     /* Start with the empty list */
     Node* head = NULL;
     
     /* Let us create a sorted linked list to test the functions
     Created linked list will be 11->11->11->13->13->20 */
     push(&head, 20);
     push(&head, 13);
     push(&head, 13);
     push(&head, 11);
     push(&head, 11);
     push(&head, 11);                                    
 
     cout<< "Linked list before duplicate removal " ;
     printList(head);
 
     /* Remove duplicates from linked list */
     removeDuplicates(head);
 
     cout<< "\nLinked list after duplicate removal " ;    
     printList(head);            
     
     return 0;
}
 
// This code is contributed by rathbhupendra

C

/* C Program to remove duplicates from a sorted linked list */
#include<stdio.h>
#include<stdlib.h>
 
/* Link list node */
struct Node
{
     int data;
     struct Node* next;
};
 
/* The function removes duplicates from a sorted list */
void removeDuplicates( struct Node* head)
{
     /* Pointer to traverse the linked list */
     struct Node* current = head;
 
     /* Pointer to store the next pointer of a node to be deleted*/
     struct Node* next_next;
   
     /* do nothing if the list is empty */
     if (current == NULL)
        return ;
 
     /* Traverse the list till last node */
     while (current->next != NULL)
     {
        /* Compare current node with next node */
        if (current->data == current->next->data)
        {
            /* The sequence of steps is important*/              
            next_next = current->next->next;
            free (current->next);
            current->next = next_next; 
        }
        else /* This is tricky: only advance if no deletion */
        {
           current = current->next;
        }
     }
}
 
/* UTILITY FUNCTIONS */
/* Function to insert a node at the beginging of the linked list */
void push( struct Node** head_ref, int new_data)
{
     /* allocate node */
     struct Node* new_node =
             ( struct Node*) malloc ( sizeof ( struct Node));
             
     /* put in the data  */
     new_node->data  = new_data;
                 
     /* link the old list off the new node */
     new_node->next = (*head_ref);    
         
     /* move the head to point to the new node */
     (*head_ref)    = new_node;
}
 
/* Function to print nodes in a given linked list */
void printList( struct Node *node)
{
     while (node!=NULL)
     {
        printf ( "%d " , node->data);
        node = node->next;
     }
}
 
/* Driver program to test above functions*/
int main()
{
     /* Start with the empty list */
     struct Node* head = NULL;
   
     /* Let us create a sorted linked list to test the functions
      Created linked list will be 11->11->11->13->13->20 */
     push(&head, 20);
     push(&head, 13);
     push(&head, 13); 
     push(&head, 11);
     push(&head, 11);
     push(&head, 11);                                   
 
     printf ( "\n Linked list before duplicate removal  " );
     printList(head);
 
     /* Remove duplicates from linked list */
     removeDuplicates(head);
 
     printf ( "\n Linked list after duplicate removal " );        
     printList(head);           
   
     return 0;
}

Java

// Java program to remove duplicates from a sorted linked list
class LinkedList
{
     Node head;  // head of list
  
     /* Linked list Node*/
     class Node
     {
         int data;
         Node next;
         Node( int d) {data = d; next = null ; }
     }
 
     void removeDuplicates()
     {
         /*Another reference to head*/
         Node curr = head;
 
         /* Traverse list till the last node */
         while (curr != null ) {
              Node temp = curr;
             /*Compare current node with the next node and
             keep on deleting them until it matches the current
             node data */
             while (temp!= null && temp.data==curr.data) {
                 temp = temp.next;
             }
             /*Set current node next to the next different
             element denoted by temp*/
             curr.next = temp;
             curr = curr.next;
         }
     }
                     
     /* Utility functions */
 
     /* Inserts a new Node at front of the list. */
     public void push( int new_data)
     {
         /* 1 & 2: Allocate the Node &
                   Put in the data*/
         Node new_node = new Node(new_data);
  
         /* 3. Make next of new Node as head */
         new_node.next = head;
  
         /* 4. Move the head to point to new Node */
         head = new_node;
     }
 
     /* Function to print linked list */
      void printList()
      {
          Node temp = head;
          while (temp != null )
          {
             System.out.print(temp.data+ " " );
             temp = temp.next;
          } 
          System.out.println();
      }
 
      /* Driver program to test above functions */
     public static void main(String args[])
     {
         LinkedList llist = new LinkedList();
         llist.push( 20 );
         llist.push( 13 );
         llist.push( 13 );
         llist.push( 11 );
         llist.push( 11 );
         llist.push( 11 );
         
         System.out.println( "List before removal of duplicates" );
         llist.printList();
         
         llist.removeDuplicates();
         
         System.out.println( "List after removal of elements" );
         llist.printList();
     }
}
/* This code is contributed by Rajat Mishra */

Python 3

# Python3 program to remove duplicate
# nodes from a sorted linked list
 
# Node class
class Node:
 
     # Constructor to initialize
     # the node object
     def __init__( self , data):
         self .data = data
         self . next = None
 
class LinkedList:
 
     # Function to initialize head
     def __init__( self ):
         self .head = None
 
     # Function to insert a new node
     # at the beginning
     def push( self , new_data):
         new_node = Node(new_data)
         new_node. next = self .head
         self .head = new_node
 
     # Given a reference to the head of a
     # list and a key, delete the first
     # occurence of key in linked list
     def deleteNode( self , key):
         
         # Store head node
         temp = self .head
 
         # If head node itself holds the
         # key to be deleted
         if (temp is not None ):
             if (temp.data = = key):
                 self .head = temp. next
                 temp = None
                 return
 
         # Search for the key to be deleted, # keep track of the previous node as
         # we need to change 'prev.next'
         while (temp is not None ):
             if temp.data = = key:
                 break
             prev = temp
             temp = temp. next
 
         # if key was not present in
         # linked list
         if (temp = = None ):
             return
 
         # Unlink the node from linked list
         prev. next = temp. next
 
         temp = None
 
     # Utility function to print the
     # linked LinkedList
     def printList( self ):
         temp = self .head
         while (temp):
             print (temp.data , end = ' ' )
             temp = temp. next
     
     # This function removes duplicates
     # from a sorted list        
     def removeDuplicates( self ):
         temp = self .head
         if temp is None :
             return
         while temp. next is not None :
             if temp.data = = temp. next .data:
                 new = temp. next . next
                 temp. next = None
                 temp. next = new
             else :
                 temp = temp. next
         return self .head
 
# Driver Code
llist = LinkedList()
 
llist.push( 20 )
llist.push( 13 )
llist.push( 13 )
llist.push( 11 )
llist.push( 11 )
llist.push( 11 )
print ( "Created Linked List: " )
llist.printList()
print ()
print ( "Linked List after removing" , "duplicate elements:" )
llist.removeDuplicates()
llist.printList()
 
# This code is contributed by
# Dushyant Pathak.

C#

// C# program to remove duplicates
// from a sorted linked list
using System;
     
public class LinkedList
{
     Node head; // head of list
 
     /* Linked list Node*/
     class Node
     {
         public int data;
         public Node next;
         public Node( int d)
         {
             data = d; next = null ;
         }
     }
 
     void removeDuplicates()
     {
         /*Another reference to head*/
         Node current = head;
 
         /* Pointer to store the next
         pointer of a node to be deleted*/
         Node next_next;
 
         /* do nothing if the list is empty */
         if (head == null )
             return ;
 
         /* Traverse list till the last node */
         while (current.next != null )
         {
 
             /*Compare current node with the next node */
             if (current.data == current.next.data)
             {
                 next_next = current.next.next;
                 current.next = null ;
                 current.next = next_next;
             }
             else // advance if no deletion
                 current = current.next;
         }
     }
                     
     /* Utility functions */
 
     /* Inserts a new Node at front of the list. */
     public void push( int new_data)
     {
         /* 1 & 2: Allocate the Node &
                 Put in the data*/
         Node new_node = new Node(new_data);
 
         /* 3. Make next of new Node as head */
         new_node.next = head;
 
         /* 4. Move the head to point to new Node */
         head = new_node;
     }
 
     /* Function to print linked list */
     void printList()
     {
         Node temp = head;
         while (temp != null )
         {
             Console.Write(temp.data+ " " );
             temp = temp.next;
         }
         Console.WriteLine();
     }
 
     /* Driver code */
     public static void Main(String []args)
     {
         LinkedList llist = new LinkedList();
         llist.push(20);
         llist.push(13);
         llist.push(13);
         llist.push(11);
         llist.push(11);
         llist.push(11);
         
         Console.WriteLine( "List before removal of duplicates" );
         llist.printList();
         
         llist.removeDuplicates();
         
         Console.WriteLine( "List after removal of elements" );
         llist.printList();
     }
}
 
/* This code is contributed by 29AjayKumar */

输出如下

Linked list before duplicate removal  11 11 11 13 13 20
Linked list after duplicate removal  11 13 20

时间复杂度：O(n)其中n是给定链表中节点的数量。

递归方法：

C ++

/* C++ Program to remove duplicates
from a sorted linked list */
#include <bits/stdc++.h>
using namespace std;
 
/* Link list node */
class Node
{
     public :
     int data;
     Node* next;
};
 
/* The function removes duplicates
from a sorted list */
void removeDuplicates(Node* head)
{
     /* Pointer to store the pointer of a node to be deleted*/
     Node* to_free;
     
     /* do nothing if the list is empty */
     if (head == NULL)
         return ;
 
     /* Traverse the list till last node */
     if (head->next != NULL)
     {
         
         /* Compare head node with next node */
         if (head->data == head->next->data)
         {
             /* The sequence of steps is important.
               to_free pointer stores the next of head
              pointer which is to be deleted.*/   
             to_free = head->next;
         head->next = head->next->next;
         free (to_free);
         removeDuplicates(head);
         }
         else /* This is tricky: only
         advance if no deletion */
         {
             removeDuplicates(head->next);
         }
     }
}
 
/* UTILITY FUNCTIONS */
/* Function to insert a node at the
beginging of the linked list */
void push(Node** head_ref, int new_data)
{
     /* allocate node */
     Node* new_node = new Node();
             
     /* put in the data */
     new_node->data = new_data;
                 
     /* link the old list off the new node */
     new_node->next = (*head_ref);    
         
     /* move the head to point to the new node */
     (*head_ref) = new_node;
}
 
/* Function to print nodes
in a given linked list */
void printList(Node *node)
{
     while (node!=NULL)
     {
         cout<< " " <<node->data;
         node = node->next;
     }
}
 
/* Driver code*/
int main()
{
     /* Start with the empty list */
     Node* head = NULL;
     
     /* Let us create a sorted linked
     list to test the functions
     Created linked list will be
     11->11->11->13->13->20 */
     push(&head, 20);
     push(&head, 13);
     push(&head, 13);
     push(&head, 11);
     push(&head, 11);
     push(&head, 11);                                    
 
     cout<< "Linked list before duplicate removal " ;
     printList(head);
 
     /* Remove duplicates from linked list */
     removeDuplicates(head);
 
     cout<< "\nLinked list after duplicate removal " ;    
     printList(head);            
     
     return 0;
}
// This code is contributed by Ashita Gupta

C

/* C recursive Program to remove duplicates from a sorted linked list */
#include<stdio.h>
#include<stdlib.h>
 
/* Link list node */
struct Node
{
     int data;
     struct Node* next;
};
/* UTILITY FUNCTIONS */
/* Function to insert a node at the beginging of the linked list */
void push( struct Node** head_ref, int new_data)
{
     /* allocate node */
     struct Node* new_node =
             ( struct Node*) malloc ( sizeof ( struct Node));
             
     /* put in the data  */
     new_node->data  = new_data;
                 
     /* link the old list off the new node */
     new_node->next = (*head_ref);    
         
     /* move the head to point to the new node */
     (*head_ref)    = new_node;
}
 
/* Function to print nodes in a given linked list */
void printList( struct Node *node)
{
     while (node!=NULL)
     {
        printf ( "%d " , node->data);
        node = node->next;
     }
}
 
  Node* deleteDuplicates(Node* head) {
         if (head == nullptr) return nullptr;
         if (head->next == nullptr) return head;
 
         if (head->data == head->next->data) {
             Node *tmp;
             // If find next element duplicate, preserve the next pointer to be deleted, // skip it, and then delete the stored one. Return head
             tmp = head->next;
             head->next = head->next->next;
             free (tmp);
             return deleteDuplicates(head);
         }
 
         else {
 
             // if doesn't find next element duplicate, leave head
             // and check from next element
             head->next = deleteDuplicates(head->next);
             return head;
         }
     }
 
int main()
{
     /* Start with the empty list */
     struct Node* head = NULL;
   
     /* Let us create a sorted linked list to test the functions
      Created linked list will be 11->11->11->13->13->20 */
     push(&head, 20);
     push(&head, 13);
     push(&head, 13); 
     push(&head, 11);
     push(&head, 11);
     push(&head, 11);                                   
 
     printf ( "\n Linked list before duplicate removal  " );
     printList(head);
 
     /* Remove duplicates from linked list */
     head = deleteDuplicates(head);
 
     printf ( "\n Linked list after duplicate removal " );        
     printList(head);           
   
     return 0;
}
/* This code is contributed by Yogesh shukla */

Java

// Java Program to remove duplicates
// from a sorted linked list
class GFG
{
/* Link list node */
static class Node
{
     int data;
     Node next;
};
 
// The function removes duplicates
// from a sorted list
static Node removeDuplicates(Node head)
{
     /* Pointer to store the pointer
     of a node to be deleted*/
     Node to_free;
     
     /* do nothing if the list is empty */
     if (head == null )
         return null ;
 
     /* Traverse the list till last node */
     if (head.next != null )
     {
         
         /* Compare head node with next node */
         if (head.data == head.next.data)
         {
             /* The sequence of steps is important.
             to_free pointer stores the next of head
             pointer which is to be deleted.*/
             to_free = head.next;
             head.next = head.next.next;
             removeDuplicates(head);
         }
         
         /* This is tricky: only advance if no deletion */
         else
         {
             removeDuplicates(head.next);
         }
     }
     return head;
}
 
/* UTILITY FUNCTIONS */
/* Function to insert a node at the beginging
of the linked list */
static Node push(Node head_ref, int new_data)
{
     /* allocate node */
     Node new_node = new Node();
             
     /* put in the data */
     new_node.data = new_data;
                 
     /* link the old list off the new node */
     new_node.next = (head_ref);    
         
     /* move the head to point to the new node */
     (head_ref) = new_node;
     return head_ref;
}
 
/* Function to print nodes in a given linked list */
static void printList(Node node)
{
     while (node != null )
     {
         System.out.print( " " + node.data);
         node = node.next;
     }
}
 
/* Driver code*/
public static void main(String args[])
{
     /* Start with the empty list */
     Node head = null ;
     
     /* Let us create a sorted linked list
     to test the functions
     Created linked list will be 11.11.11.13.13.20 */
     head = push(head, 20 );
     head = push(head, 13 );
     head = push(head, 13 );
     head = push(head, 11 );
     head = push(head, 11 );
     head = push(head, 11 );                                    
 
     System.out.println( "Linked list before" +
                       " duplicate removal " );
     printList(head);
 
     /* Remove duplicates from linked list */
     head = removeDuplicates(head);
 
     System.out.println( "\nLinked list after" +
                        " duplicate removal " );    
     printList(head);            
}
} 
 
// This code is contributed by Arnab Kundu

Python3

# Python3 Program to remove duplicates
# from a sorted linked list
import math
 
# Link list node
class Node:
     def __init__( self , data):
         self .data = data
         self . next = None
 
# The function removes duplicates
# from a sorted list
def removeDuplicates(head):
     
     # Pointer to store the pointer of a node
     # to be deleted to_free
     
     # do nothing if the list is empty
     if (head = = None ):
         return
 
     # Traverse the list till last node
     if (head. next ! = None ):
         
         # Compare head node with next node
         if (head.data = = head. next .data):
             
             # The sequence of steps is important.
             # to_free pointer stores the next of head
             # pointer which is to be deleted.
             to_free = head. next
             head. next = head. next . next
             
             # free(to_free)
             removeDuplicates(head)
         
         # This is tricky: only advance if no deletion
         else :
             removeDuplicates(head. next )
         
     return head
 
# UTILITY FUNCTIONS
# Function to insert a node at the
# beginging of the linked list
def push(head_ref, new_data):
     
     # allocate node
     new_node = Node(new_data)
             
     # put in the data
     new_node.data = new_data
                 
     # link the old list off the new node
     new_node. next = head_ref    
         
     # move the head to point to the new node
     head_ref = new_node
     return head_ref
 
# Function to print nodes in a given linked list
def printList(node):
     while (node ! = None ):
         print (node.data, end = " " )
         node = node. next
     
# Driver code
if __name__ = = '__main__' :
 
     # Start with the empty list
     head = None
     
     # Let us create a sorted linked list
     # to test the functions
     # Created linked list will be 11.11.11.13.13.20
     head = push(head, 20 )
     head = push(head, 13 )
     head = push(head, 13 )
     head = push(head, 11 )
     head = push(head, 11 )
     head = push(head, 11 )                                
 
     print ( "Linked list before duplicate removal " , end = "")
     printList(head)
 
     # Remove duplicates from linked list
     removeDuplicates(head)
 
     print ( "\nLinked list after duplicate removal " , end = "")
     printList(head)        
     
# This code is contributed by Srathore

C#

// C# Program to remove duplicates
// from a sorted linked list
using System;
     
class GFG
{
/* Link list node */
public class Node
{
     public int data;
     public Node next;
};
 
// The function removes duplicates
// from a sorted list
static Node removeDuplicates(Node head)
{
     /* Pointer to store the pointer
     of a node to be deleted*/
     Node to_free;
     
     /* do nothing if the list is empty */
     if (head == null )
         return null ;
 
     /* Traverse the list till last node */
     if (head.next != null )
     {
         
         /* Compare head node with next node */
         if (head.data == head.next.data)
         {
             /* The sequence of steps is important.
             to_free pointer stores the next of head
             pointer which is to be deleted.*/
             to_free = head.next;
             head.next = head.next.next;
             removeDuplicates(head);
         }
         
         /* This is tricky: only advance if no deletion */
         else
         {
             removeDuplicates(head.next);
         }
     }
     return head;
}
 
/* UTILITY FUNCTIONS */
/* Function to insert a node at the beginging
of the linked list */
static Node push(Node head_ref, int new_data)
{
     /* allocate node */
     Node new_node = new Node();
             
     /* put in the data */
     new_node.data = new_data;
                 
     /* link the old list off the new node */
     new_node.next = (head_ref);    
         
     /* move the head to point to the new node */
     (head_ref) = new_node;
     return head_ref;
}
 
/* Function to print nodes in
a given linked list */
static void printList(Node node)
{
     while (node != null )
     {
         Console.Write( " " + node.data);
         node = node.next;
     }
}
 
// Driver code
public static void Main(String []args)
{
     /* Start with the empty list */
     Node head = null ;
     
     /* Let us create a sorted linked list
     to test the functions
     Created linked list will be 11.11.11.13.13.20 */
     head = push(head, 20);
     head = push(head, 13);
     head = push(head, 13);
     head = push(head, 11);
     head = push(head, 11);
     head = push(head, 11);                                    
 
     Console.Write( "Linked list before" +
                   " duplicate removal " );
     printList(head);
 
     /* Remove duplicates from linked list */
     head = removeDuplicates(head);
 
     Console.Write( "\nLinked list after" +
                   " duplicate removal " );    
     printList(head);            
}
}
 
// This code is contributed by PrinciRaj1992

输出如下

Linked list before duplicate removal  11 11 11 13 13 20
Linked list after duplicate removal  11 13 20

另一种方法：创建一个指针, 该指针指向每个元素的第一个出现位置, 另一个指针temp指向每个元素, 当前一个指针的值不等于temp指针时, 我们将前一个指针的指针设置为第一次出现另一个节点。

下面是上述方法的实现：

Java

// Java program to remove duplicates
// from a sorted linked list
class LinkedList
{
     // head of list
     Node head;
  
     // Linked list Node
     class Node
     {
         int data;
         Node next;
         Node( int d) {
           data = d;
           next = null ;
         }
     }
 
     // Function to remove duplicates
     // from the given linked list
     void removeDuplicates()
     {
         // Two references to head
         // temp will iterate to the
         // whole Linked List
         // prev will point towards
         // the first occurence of every element
         Node temp = head, prev=head;
 
         // Traverse list till the last node
         while (temp != null ) {
            
            // Compare values of both pointers
            if (temp.data!=prev.data)
            {
              /* if the value of prev is
              not equal to the value of
              temp that means there are no
              more occruences of the prev data.
              So we can set the next of
              prev to the temp node.*/
              prev.next=temp;
              prev=temp;
            }
             /*Set the temp to the next node*/
             temp=temp.next;
         }
       /*This is the edge case if there
       are more than one occurrences
       of the last element*/
       if (prev!=temp){
             prev.next= null ;
         }
     }
                     
     /* Utility functions */
 
     /* Inserts a new Node at front of the list. */
     public void push( int new_data)
     {
         /* 1 & 2: Allocate the Node &
                   Put in the data*/
         Node new_node = new Node(new_data);
  
         /* 3. Make next of new Node as head */
         new_node.next = head;
  
         /* 4. Move the head to point to new Node */
         head = new_node;
     }
 
     /* Function to print linked list */
      void printList()
      {
          Node temp = head;
          while (temp != null )
          {
             System.out.print(temp.data+ " " );
             temp = temp.next;
          } 
          System.out.println();
      }
 
      /* Driver program to test above functions */
     public static void main(String args[])
     {
         LinkedList llist = new LinkedList();
         llist.push( 20 );
         llist.push( 13 );
         llist.push( 13 );
         llist.push( 11 );
         llist.push( 11 );
         llist.push( 11 );
         
         System.out.print( "List before " );
         System.out.println( "removal of duplicates" );
         llist.printList();
         
         llist.removeDuplicates();
         
         System.out.println( "List after removal of elements" );
         llist.printList();
     }
}
/* This code is contributed by Arshita */

输出如下

List before removal of duplicates
11 11 11 13 13 20 
List after removal of elements
11 13 20

相关文章：

从排序的链表中删除所有重复项

参考文献：

cslibrary.stanford.edu/105/LinkedListProblems.pdf

木子山

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