java - 从未排序的链表中删除重复项

Question

import java.util.*;
/*
 *  Remove duplicates from an unsorted linked list
 */
public class LinkedListNode {  
    public int data;  
    public LinkedListNode next;  

    public LinkedListNode(int data) {  
        this.data = data;    
    }  
}

public class Task {
    public static void deleteDups(LinkedListNode head){
      Hashtable<Integer, Boolean> table=new Hashtable<Integer, Boolean>();
      LinkedListNode previous=null;
      //nth node is not null
      while(head!=null){
        //have duplicate
            if(table.containsKey(head.data)){
                            //skip duplicate
                previous.next=head.next;
            }else{
            //put the element into hashtable
            table.put(head.data,true);
            //move to the next element
            previous=head;
            }
      //iterate
      head=head.next;
      }
   }
   public static void main (String args[]){
       LinkedList<Integer> list=new LinkedList<Integer>();
       list.addLast(1);
       list.addLast(2);
       list.addLast(3);
       list.addLast(3);
       list.addLast(3);
       list.addLast(4);
       list.addLast(4);
       System.out.println(list);
       LinkedListNode head=new LinkedListNode(list.getFirst());
       Task.deleteDups(head);
       System.out.println(list);
   }
}

结果： [1, 2, 3, 3, 3, 4, 4] [1, 2, 3, 3, 3, 4, 4]

它不会消除重复项。

为什么方法不起作用？

score 11 · Accepted Answer

遍历链表，将每个元素添加到哈希表中。当我们发现重复元素时，我们删除该元素并继续迭代。由于我们使用的是链表，因此我们可以一次性完成所有操作。

以下解决方案需要 O(n) 时间，n 是链表中元素的数量。

public static void deleteDups (LinkedListNode n){
  Hashtable table = new Hashtable();
  LinkedListNode previous = null;
  while(n!=null){
      if(table.containsKey(n.data)){
          previous.next = n.next;
      } else {
          table.put(n.data, true);
          previous = n;
      }
      n = n.next;
  }
}

score 6 · Accepted Answer

您提供的解决方案不会修改原始列表。
要修改原始列表并删除重复项，我们可以使用两个指针进行迭代。Current：遍历 LinkedList，而 runner 则检查所有后续节点是否有重复项。

下面的代码在 O(1) 空间中运行，但在 O(N 平方) 时间内运行。

公共无效deleteDups（LinkedListNode头）{

if(head == null)
    return;

LinkedListNode currentNode = head;       
while(currentNode!=null){
    LinkedListNode runner = currentNode;
    while(runner.next!=null){
        if(runner.next.data == currentNode.data)
            runner.next = runner.next.next;
        else
            runner = runner.next;
    }
    currentNode = currentNode.next;
}

}

参考 : Gayle laakmann mcdowell

score 3 · Accepted Answer

这是在java中执行此操作的两种方法。上面使用的方法在 O(n) 中有效，但需要额外的空间。第二个版本在 O(n^2) 中运行但不需要额外的空间。

import java.util.Hashtable;

public class LinkedList {
LinkedListNode head;

public static void main(String args[]){
    LinkedList list = new LinkedList();
    list.addNode(1);
    list.addNode(1);
    list.addNode(1);
    list.addNode(2);
    list.addNode(3);
    list.addNode(2);

    list.print();
    list.deleteDupsNoStorage(list.head);
    System.out.println();
    list.print();
}

public void print(){
    LinkedListNode n = head;
    while(n!=null){
        System.out.print(n.data +" ");
        n = n.next;
    }
}

public void deleteDups(LinkedListNode n){
    Hashtable<Integer, Boolean> table = new Hashtable<Integer, Boolean>();
    LinkedListNode prev = null;

    while(n !=null){
        if(table.containsKey(new Integer(n.data))){
            prev.next = n.next;     //skip the previously stored references next node
        }else{
            table.put(new Integer(n.data) , true);
            prev = n;       //stores a reference to n
        }

        n = n.next;
    }
}

public void deleteDupsNoStorage(LinkedListNode n){
    LinkedListNode current = n;

    while(current!=null){
        LinkedListNode runner = current;
        while(runner.next!=null){
            if(runner.next.data == current.data){
                runner.next = runner.next.next;
            }else{
                runner = runner.next;
            }
        }
        current = current.next;
    }

}

public void addNode(int d){
    LinkedListNode n = new LinkedListNode(d);
    if(this.head==null){
        this.head = n;
    }else{
        n.next = head;
        head = n;
    }
}

private class LinkedListNode{
    LinkedListNode next;
    int data;

    public LinkedListNode(int d){
        this.data = d;
    }
}
}

score 2 · Accepted Answer

您可以使用以下 java 方法删除重复项：

1)complexity O ( n^2)

public void removeDuplicate(Node head) {
    Node temp = head;
    Node duplicate = null;                //will point to duplicate node
    Node prev = null;                     //prev node to duplicate node
    while (temp != null) {                //iterate through all nodes       
        Node curr = temp;
        while (curr != null) {                     //compare each one by one
            /*in case of duplicate skip the node by using prev node*/
            if (curr.getData() == temp.getData() && temp != curr) {        
                duplicate = curr;
                prev.setNext(duplicate.getNext());
            }
            prev = curr;
            curr = curr.getNext();
        }
        temp = temp.getNext();
    }
}

输入：1=>2=>3=>5=>5=>1=>3=>

输出：1=>2=>3=>5=>

2）使用散列表complexity的O（n）。

public void removeDuplicateUsingMap(Node head) {
    Node temp = head;
    Map<Integer, Boolean> hash_map = new HashMap<Integer, Boolean>(); //create a hash map
    while (temp != null) {  
        if (hash_map.get(temp.getData()) == null) {  //if key is not set then set is false
            hash_map.put(temp.getData(), false);
        } else {                                   //if key is already there,then delete the node
            deleteNode(temp,head);
        }
        temp = temp.getNext();
    }

}

public void deleteNode(Node n, Node start) {
        Node temp = start;
        if (n == start) {
            start = null;
        } else {
            while (temp.getNext() != n) {
                temp = temp.getNext();
            }

            temp.setNext(n.getNext());

        }
    }

输入：1=>2=>3=>5=>5=>1=>3=>

输出：1=>2=>3=>5=>

score 1 · Accepted Answer

这是一个非常简单的版本。

LinkedList<Integer> a = new LinkedList<Integer>(){{
  add(1);
  add(1);
}}
Set<Integer> set = new HashSet<Integer>(a);
a = new LinkedList<Integer>(set);

非常简洁。不是吗？

score 1 · Accepted Answer

试试这个，它可以从你的linkedList中删除重复的元素

package com.loknath.lab;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Set;

public class Task {
    public static void main(String[] args) {

        LinkedList<Integer> list = new LinkedList<Integer>();
        list.addLast(1);
        list.addLast(2);
        list.addLast(3);
        list.addLast(3);
        list.addLast(3);
        list.addLast(4);
        list.addLast(4);
        deleteDups(list);
        System.out.println(list);
    }

    public static void deleteDups(LinkedList<Integer> list) {
        Set s = new HashSet<Integer>();
        s.addAll(list);
        list.clear();
        list.addAll(s);

    }
}

score 1 · Accepted Answer

Ans 在 C 中。首先在 nlog 时间内对链表 sort() 进行排序，然后删除重复的 del_dip() 。

node * partition(node *start)
{
    node *l1=start;
    node *temp1=NULL;
    node *temp2=NULL;
    if(start->next==NULL)
        return start;

    node * l2=f_b_split(start);
      if(l1->next!=NULL)
        temp1=partition(l1);
      if(l2->next!=NULL)
            temp2=partition(l2);

if(temp1==NULL || temp2==NULL)
    {
        if(temp1==NULL && temp2==NULL)
        temp1=s_m(l1,l2);

        else if(temp1==NULL)
        temp1=s_m(l1,temp2);

        else if(temp2==NULL)
        temp1=s_m(temp1,l2);
}
    else
            temp1=s_m(temp1,temp2);

    return temp1;
}

node * sort(node * start)
{
    node * temp=partition(start);
        return temp;
}

void del_dup(node * start)
{
  node * temp;
    start=sort(start);
    while(start!=NULL)
        {
        if(start->next!=NULL && start->data==start->next->data  )
            {
                temp=start->next;
                start->next=start->next->next;
                free(temp);
            continue;
            }
        start=start->next;
        }
}

void main()
 {
    del_dup(list1);
    print(list1);
}

score 1 · Accepted Answer

I think you can just use one iterator current to finish this problem 

public void compress(){
    ListNode current = front;
    HashSet<Integer> set = new HashSet<Integer>();
    set.add(current.data);
    while(current.next != null){
       if(set.contains(current.next.data)){
          current.next = current.next.next;         }
         else{
            set.add(current.next.data);
            current = current.next;
         }
      }

}

score 0 · Accepted Answer

试试这个。它的工作。// 删除链表中的重复项

import java.io.*;
import java.util.*;
import java.text.*;
class LinkedListNode{
    int data;
    LinkedListNode next=null;

    public LinkedListNode(int d){
        data=d;
    }
    void appendToTail(int d){
        LinkedListNode newnode = new LinkedListNode(d);
        LinkedListNode n=this;
        while(n.next!=null){
            n=n.next;
        }
        n.next=newnode;
    }

    void print(){
        LinkedListNode n=this;
        System.out.print("Linked List: ");
        while(n.next!=null){
            System.out.print(n.data+" -> ");
            n=n.next;
        }
        System.out.println(n.data);
    }
}
class LinkedList2_0
{
    public static void deletenode2(LinkedListNode head,int d){
        LinkedListNode n=head;
        // If It's head node
        if(n.data==d){
            head=n.next;
        }
        //If its other
        while(n.next!=null){
            if(n.next.data==d){
                n.next=n.next.next;
            }
            n=n.next;
        }
    }

    public static void removeDuplicateWithBuffer(LinkedListNode head){
        LinkedListNode n=head;
        LinkedListNode prev=null;
        Hashtable<Integer, Boolean> table = new Hashtable<Integer, Boolean>();
        while(n!=null){
            if(table.containsKey(n.data)){
                prev.next=n.next;
            }
            else{
                table.put(n.data,true);
                prev=n;
            }
            n=n.next;
        }
    }
    public static void removeDuplicateWithoutBuffer(LinkedListNode head){
        LinkedListNode currentNode=head;
        while(currentNode!=null){
            LinkedListNode runner=currentNode;
            while(runner.next!=null){
                if(runner.next.data==currentNode.data){
                    runner.next=runner.next.next;
                }
                else
                    runner=runner.next;
            }
            currentNode=currentNode.next;
        }
    }
    public static void main(String[] args) throws java.lang.Exception {
        LinkedListNode head=new LinkedListNode(1);
        head.appendToTail(1);
        head.appendToTail(3);
        head.appendToTail(2);
        head.appendToTail(3);
        head.appendToTail(4);
        head.appendToTail(5);
        head.print();

        System.out.print("After Delete: ");
        deletenode2(head,4);
        head.print();

        //System.out.print("After Removing Duplicates(with buffer): ");
        //removeDuplicateWithBuffer(head);
        //head.print();

        System.out.print("After Removing Duplicates(Without buffer): ");
        removeDuplicateWithoutBuffer(head);
        head.print();

    }
}

score 0 · Accepted Answer

这里有几个其他的解决方案（与 Cracking coding inerview 略有不同，更易于阅读 IMO）。

public void deleteDupes(Node head) {

Node current = head;
while (current != null) {
    Node next = current.next;
    while (next != null) {
        if (current.data == next.data) {
            current.next = next.next;
            break;
        }

        next = next.next;
    }

    current = current.next;
}

}

public void deleteDupes(Node head) {
Node current = head;
while (current != null) {
    Node next = current.next;
    while (next != null) {
        if (current.data == next.data) {
            current.next = next.next;
            current = current.next;
            next = current.next;
        } else {
            next = next.next;
        }
    }

    current = current.next;
}

}

score 0 · Accepted Answer

第一个问题是

LinkedListNode head=new LinkedListNode(list.getFirst());

实际上并没有head使用list. list.getFirst()简单地返回 Integer 1，并head包含1它的唯一元素。您必须head通过循环进行初始化list才能获取所有元素。

此外，虽然

Task.deleteDups(head)

修改head，这list完全保持不变 - 没有理由将更改head传播到list。因此，要检查您的方法，您必须循环head并打印出每个元素，而不是list再次打印出来。

score 0 · Accepted Answer

/**
*
* Remove duplicates from an unsorted linked list.
*/
public class RemoveDuplicates {
    public static void main(String[] args) {
        LinkedList<String> list = new LinkedList<String>();
        list.add("Apple");
        list.add("Grape");
        list.add("Apple");
        HashSet<String> set = removeDuplicatesFromList(list);
        System.out.println("Removed duplicates" + set);
    }
    public static HashSet<String> removeDuplicatesFromList(LinkedList<String> list){
        HashSet<String> set = new LinkedHashSet<String>();
        set.addAll(list);
        return set;
    }
}

score 0 · Accepted Answer

这是没有 HashSet 或创建节点的简单方法。

public String removeDuplicates(String str) {
    LinkedList<Character> chars = new LinkedList<Character>();

    for(Character c: str.toCharArray()){
        chars.add(c);
    }

    for (int i = 0; i < chars.size(); i++){
        for (int j = i+1; j < chars.size(); j++){
            if(chars.get(j) == chars.get(i)){
                chars.remove(j);
                j--;
            }
        }
    }

    return new String(chars.toString());
}

并验证它：

@Test
public void verifyThatNoDuplicatesInLinkedList(){
    CodeDataStructures dataStructures = new CodeDataStructures();

    assertEquals("abcdefghjk", dataStructures.removeDuplicates("abcdefgabcdeaaaaaaaaafabcdeabcdefgabcdbbbbbbefabcdefghjkabcdefghjkghjkhjkabcdefghabcdefghjkjfghjkabcdefghjkghjkhjkabcdefghabcdefghjkj")
            .replace(",", "")
            .replace("]", "")
            .replace("[", "")
            .replace(" ", ""));
}

score 0 · Accepted Answer

上面给出的所有解决方案看起来都经过优化，但大多数都将自定义节点定义为解决方案的一部分。这是一个使用 Java 的LinkedList和HashSet的简单实用的解决方案，它不限于使用预先存在的库和方法。

时间复杂度：O(n)

空间复杂度：O(n)

@SuppressWarnings({ "unchecked", "rawtypes" })
private static LinkedList<?> removeDupsUsingHashSet(LinkedList<?> list) {

    HashSet set = new HashSet<>();
    for (int i = 0; i < list.size();) {
        if (set.contains(list.get(i))) {
            list.remove(i);
            continue;
        } else {
            set.add(list.get(i));
            i++;
        }
    }
    return list;
}

这也保留了列表顺序。

score 0 · Accepted Answer

public static void main(String[] args) {

    LinkedList<Integer> linkedList = new LinkedList<>();
    linkedList.add(1);
    linkedList.add(2);
    linkedList.add(2);
    linkedList.add(3);
    linkedList.add(4);
    linkedList.add(5);
    linkedList.add(6);
    deleteElement(linkedList);
    System.out.println(linkedList);
}

private static void deleteElement(LinkedList<Integer> linkedList) {

    Set s = new HashSet<Integer>();

    s.addAll(linkedList);
    linkedList.clear();
    linkedList.addAll(s);

}

score 0 · Accepted Answer

这是我的 Java 版本

//  Remove duplicate from a sorted linked list
public void removeDuplicates() {

        Node current = head;
        Node next = null;
        /* Traverse list till the last node */
        while (current != null) {
            next = current;

            /*
             * Compare current node with the next node and keep on deleting them until it
             * matches the current node data
             */
            while (next != null && current.getValue() == next.getValue()) {

                next = next.getNext();

            }

            /*
             * Set current node next to the next different element denoted by temp
             */
            current.setNext(next);
            current = current.getNext();
        }
    }

score 0 · Accepted Answer

下面的代码在不需要任何临时缓冲区的情况下实现了这一点。它首先比较第一个和第二个节点，如果不匹配，它将第一个节点的字符添加到第二个节点，然后继续将第二个节点中的所有字符与第三个节点的字符进行比较，依此类推。完成后，在离开节点之前，它会清除添加的所有内容并恢复其位于 node.val.char(0) 的旧值

F > FO > FOL > (找到匹配，node.next = node.next.next) > (再次匹配，丢弃) > FOLW > ....

public void onlyUnique(){
        Node node = first;
        while(node.next != null){
            for(int i = 0 ; i < node.val.length(); i++){
                if(node.val.charAt(i) == node.next.val.charAt(0)){
                    node.next = node.next.next;
                }else{
                    if(node.next.next != null){ //no need to copy everything to the last element
                        node.next.val = node.next.val + node.val;
                    }
                    node.val = node.val.charAt(0)+ "";
                }
            }
            node = node.next;
        }
    }

score 0 · Accepted Answer

LinkedList<Node> list = new LinkedList<Node>();

 for(int i=0; i<list.size(); i++){
        for(int j=0; j<list.size(); j++){
            if(list.get(i).data == list.get(j).data && i!=j){
                if(i<j){
                     list.remove(j);
                    if(list.get(j)!= null){
                         list.get(j-1).next = list.get(j);
                    }else{
                        list.get(j-1).next = null;
                    }

                }
                else{
                    if(i>j){
                        list.remove(i);
                        if(list.get(i) != null){
                            list.get(j).next = list.get(i);
                        }else{
                            list.get(j).next = null;
                        }

                    }
                }

            }

        }
    }

score -1 · Accepted Answer

1.完全动态的方法 2.从 LinkedList 中删除重复项 3. LinkedList 基于动态对象的创建 谢谢

import java.util.Scanner;
class Node{
    int data;
    Node next;
    public Node(int data)
    {
        this.data=data;
        this.next=null;
    }
}
class Solution
{
    public static Node insert(Node head,int data)
    {
    Node p=new Node(data);
    if(head==null)
    {
        head=p;
    }
    else if(head.next==null)
    {
        head.next=p;
    }
    else
    {
        Node start=head;
        while(start.next!=null)
        {
            start=start.next;   
        }
        start.next=p;
        return head;
        //System.out.println();
    }
    return head;    
    }
    public static void display(Node head)
    {
        Node start=head;
        while(start!=null)
        {
            System.out.print(start.data+" ");
            start=start.next;
        }

    }
    public static Node remove_duplicates(Node head)
    {
       if(head==null||head.next==null)
       {
           return head;
       }
       Node prev=head;
       Node p=head.next;

       while(p!=null)
       {
           if(p.data==prev.data)
           {
            prev.next=p.next;
            p=p.next;              
           }
           else{
               prev=p;
               p=p.next;   
           }
       }
       return head;
    }
    public static void main(String args[])
    {
        Scanner sc=new Scanner(System.in);
        Node head=null;
        int T=sc.nextInt();
        while(T-->0)
        {
            int ele=sc.nextInt();
            head=insert(head,ele);
        }
        head=remove_duplicates(head);
        display(head);  
    }
}

输入：5 1 1 2 3 3 输出：1 2 3

java - 从未排序的链表中删除重复项

19 回答 19

Related

Reference