删除右侧值较大的节点
给定一个单向链表，删除右侧所有具有较大值的节点。
例子：
a)列表 12->15->10->11->5->6->2->3->NULL 应更改为 15->11->6->3->NULL。注意12、10、5、2已经被删掉了，因为右边有更大的值。
当我们检查12时，我们看到12之后有一个值大于12（即15）的节点，所以我们删除12。
当我们检查 15 时，我们发现 15 之后没有节点的值大于 15，所以我们保留这个节点。
当我们这样做时，我们得到 15->6->3
b)列表 10->20->30->40->50->60->NULL 应更改为 60->NULL。请注意，10、20、30、40 和 50 已被删除，因为它们在右侧都有更大的值。
c)列表 60->50->40->30->20->10->NULL 不应更改。
方法一（简单）
使用两个循环。在外循环中，一一选取链表的节点。在内部循环中，检查是否存在值大于选取的节点的节点。如果存在值更大的节点，则删除选取的节点。
时间复杂度： O(n^2)
方法二（反向使用）
感谢 Paras 提供以下算法。
1. 反转列表。
2. 遍历反向列表。保持最大到现在。如果下一个节点小于max，则删除下一个节点，否则max=下一个节点。
3. 再次反转列表以保留原始顺序。
时间复杂度： O(n)
感谢 R.Srinivasan 提供以下代码。
C++
// C++ program to delete nodes
// which have a greater value on
// right side
#include
using namespace std;
/* structure of a linked list node */
struct Node
{
int data;
struct Node* next;
};
/* prototype for utility functions */
void reverseList(struct Node** headref);
void _delLesserNodes(struct Node* head);
/* Deletes nodes which have a node with
greater value node on left side */
void delLesserNodes(struct Node** head_ref)
{
/* 1) Reverse the linked list */
reverseList(head_ref);
/* 2) In the reversed list, delete nodes
which have a node with greater value node
on left side. Note that head node is never
deleted because it is the leftmost node.*/
_delLesserNodes(*head_ref);
/* 3) Reverse the linked list again to
retain the original order */
reverseList(head_ref);
}
/* Deletes nodes which have
greater value node(s) on left side */
void _delLesserNodes(struct Node* head)
{
struct Node* current = head;
/* Initialize max */
struct Node* maxnode = head;
struct Node* temp;
while (current != NULL &&
current->next != NULL)
{
/* If current is smaller than max,
then delete current */
if (current->next->data < maxnode->data)
{
temp = current->next;
current->next = temp->next;
free(temp);
}
/* If current is greater than max,
then update max and move current */
else
{
current = current->next;
maxnode = current;
}
}
}
/* Utility function to insert a node
at the beginning */
void push(struct Node** head_ref, int new_data)
{
struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
new_node->data = new_data;
new_node->next = *head_ref;
*head_ref = new_node;
}
/* Utility function to reverse a linked list */
void reverseList(struct Node** headref)
{
struct Node* current = *headref;
struct Node* prev = NULL;
struct Node* next;
while (current != NULL)
{
next = current->next;
current->next = prev;
prev = current;
current = next;
}
*headref = prev;
}
/* Utility function to print a linked list */
void printList(struct Node* head)
{
while (head != NULL)
{
cout << " " << head->data ;
head = head->next;
}
cout << "\n" ;
}
/* Driver program to test above functions */
int main()
{
struct Node* head = NULL;
/* Create following linked list
12->15->10->11->5->6->2->3 */
push(&head, 3);
push(&head, 2);
push(&head, 6);
push(&head, 5);
push(&head, 11);
push(&head, 10);
push(&head, 15);
push(&head, 12);
cout << "Given Linked List \n" ;
printList(head);
delLesserNodes(&head);
cout << "Modified Linked List \n" ;
printList(head);
return 0;
}
// This code is contributed by shivanisinghss2110 C
// C program to delete nodes which have a greater value on
// right side
#include
#include
/* structure of a linked list node */
struct Node {
int data;
struct Node* next;
};
/* prototype for utility functions */
void reverseList(struct Node** headref);
void _delLesserNodes(struct Node* head);
/* Deletes nodes which have a node with greater value node
on left side */
void delLesserNodes(struct Node** head_ref)
{
/* 1) Reverse the linked list */
reverseList(head_ref);
/* 2) In the reversed list, delete nodes which have a node
with greater value node on left side. Note that head
node is never deleted because it is the leftmost node.*/
_delLesserNodes(*head_ref);
/* 3) Reverse the linked list again to retain the
original order */
reverseList(head_ref);
}
/* Deletes nodes which have greater value node(s) on left side */
void _delLesserNodes(struct Node* head)
{
struct Node* current = head;
/* Initialize max */
struct Node* maxnode = head;
struct Node* temp;
while (current != NULL && current->next != NULL) {
/* If current is smaller than max, then delete current */
if (current->next->data < maxnode->data) {
temp = current->next;
current->next = temp->next;
free(temp);
}
/* If current is greater than max, then update max and
move current */
else {
current = current->next;
maxnode = current;
}
}
}
/* Utility function to insert a node at the beginning */
void push(struct Node** head_ref, int new_data)
{
struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
new_node->data = new_data;
new_node->next = *head_ref;
*head_ref = new_node;
}
/* Utility function to reverse a linked list */
void reverseList(struct Node** headref)
{
struct Node* current = *headref;
struct Node* prev = NULL;
struct Node* next;
while (current != NULL) {
next = current->next;
current->next = prev;
prev = current;
current = next;
}
*headref = prev;
}
/* Utility function to print a linked list */
void printList(struct Node* head)
{
while (head != NULL) {
printf("%d ", head->data);
head = head->next;
}
printf("\n");
}
/* Driver program to test above functions */
int main()
{
struct Node* head = NULL;
/* Create following linked list
12->15->10->11->5->6->2->3 */
push(&head, 3);
push(&head, 2);
push(&head, 6);
push(&head, 5);
push(&head, 11);
push(&head, 10);
push(&head, 15);
push(&head, 12);
printf("Given Linked List \n");
printList(head);
delLesserNodes(&head);
printf("Modified Linked List \n");
printList(head);
return 0;
} Java
// Java program to delete nodes which have a greater value on
// right side
class LinkedList {
Node head; // head of list
/* Linked list Node*/
class Node {
int data;
Node next;
Node(int d)
{
data = d;
next = null;
}
}
/* Deletes nodes which have a node with greater
value node on left side */
void delLesserNodes()
{
/* 1.Reverse the linked list */
reverseList();
/* 2) In the reversed list, delete nodes which
have a node with greater value node on left
side. Note that head node is never deleted
because it is the leftmost node.*/
_delLesserNodes();
/* 3) Reverse the linked list again to retain
the original order */
reverseList();
}
/* Deletes nodes which have greater value node(s)
on left side */
void _delLesserNodes()
{
Node current = head;
/* Initialise max */
Node maxnode = head;
Node temp;
while (current != null && current.next != null) {
/* If current is smaller than max, then delete
current */
if (current.next.data < maxnode.data) {
temp = current.next;
current.next = temp.next;
temp = null;
}
/* If current is greater than max, then update
max and move current */
else {
current = current.next;
maxnode = current;
}
}
}
/* Utility functions */
/* Inserts a new Node at front of the list. */
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 reverse the linked list */
void reverseList()
{
Node current = head;
Node prev = null;
Node next;
while (current != null) {
next = current.next;
current.next = prev;
prev = current;
current = next;
}
head = prev;
}
/* Function to print linked list */
void printList()
{
Node temp = head;
while (temp != null) {
System.out.print(temp.data + " ");
temp = temp.next;
}
System.out.println();
}
/* Drier program to test above functions */
public static void main(String args[])
{
LinkedList llist = new LinkedList();
/* Constructed Linked List is 12->15->10->11->
5->6->2->3 */
llist.push(3);
llist.push(2);
llist.push(6);
llist.push(5);
llist.push(11);
llist.push(10);
llist.push(15);
llist.push(12);
System.out.println("Given Linked List");
llist.printList();
llist.delLesserNodes();
System.out.println("Modified Linked List");
llist.printList();
}
} /* This code is contributed by Rajat Mishra */C#
// C# program to delete nodes which have a greater value on
// right side
using System;
class LinkedList
{
public 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;
}
}
/* Deletes nodes which have a node with greater
value node on left side */
void delLesserNodes()
{
/* 1.Reverse the linked list */
reverseList();
/* 2) In the reversed list, delete nodes which
have a node with greater value node on left
side. Note that head node is never deleted
because it is the leftmost node.*/
_delLesserNodes();
/* 3) Reverse the linked list again to retain
the original order */
reverseList();
}
/* Deletes nodes which have greater value node(s)
on left side */
void _delLesserNodes()
{
Node current = head;
/* Initialise max */
Node maxnode = head;
Node temp;
while (current != null && current.next != null)
{
/* If current is smaller than max, then delete
current */
if (current.next.data < maxnode.data)
{
temp = current.next;
current.next = temp.next;
temp = null;
}
/* If current is greater than max, then update
max and move current */
else
{
current = current.next;
maxnode = current;
}
}
}
/* Utility functions */
/* Inserts a new Node at front of the list. */
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 reverse the linked list */
void reverseList()
{
Node current = head;
Node prev = null;
Node next;
while (current != null)
{
next = current.next;
current.next = prev;
prev = current;
current = next;
}
head = prev;
}
/* Function to print linked list */
void printList()
{
Node temp = head;
while (temp != null)
{
Console.Write(temp.data + " ");
temp = temp.next;
}
Console.WriteLine();
}
/* Drier program to test above functions */
public static void Main(string []args)
{
LinkedList llist = new LinkedList();
/* Constructed Linked List is 12->15->10->11->
5->6->2->3 */
llist.push(3);
llist.push(2);
llist.push(6);
llist.push(5);
llist.push(11);
llist.push(10);
llist.push(15);
llist.push(12);
Console.WriteLine("Given Linked List");
llist.printList();
llist.delLesserNodes();
Console.WriteLine("Modified Linked List");
llist.printList();
}
}
// This code is contributed by pratham76Javascript
Java
// Java program for above approach
import java.io.*;
// This class represents a single node
// in a linked list
class Node {
int data;
Node next;
public Node(int data){
this.data = data;
this.next = null;
}
}
//This is a utility class for linked list
class LLUtil{
// This function creates a linked list from a
// given array and returns head
public Node createLL(int[] arr){
Node head = new Node(arr[0]);
Node temp = head;
Node newNode = null;
for(int i = 1; i < arr.length; i++){
newNode = new Node(arr[i]);
temp.next = newNode;
temp = temp.next;
}
return head;
}
//This function prints given linked list
public void printLL(Node head){
while(head != null){
System.out.print(head.data + " ");
head = head.next;
}
System.out.println();
}
}
class GFG {
public static void main (String[] args) {
int[] arr = {12,15,10,11,5,6,2,3};
LLUtil llu = new LLUtil();
Node head = llu.createLL(arr);
System.out.println("Given Linked List");
llu.printLL(head);
head = deleteNodesOnRightSide(head);
System.out.println("Modified Linked List");
llu.printLL(head);
}
//Main function
public static Node deleteNodesOnRightSide(Node head){
if(head == null || head.next == null) return head;
Node nextNode = deleteNodesOnRightSide(head.next);
if(nextNode.data > head.data) return nextNode;
head.next = nextNode;
return head;
}
}C#
// C# program for above approach
using System;
// This class represents a single node
// in a linked list
class Node
{
public int data;
public Node next;
public Node(int data)
{
this.data = data;
this.next = null;
}
}
// This is a utility class for linked list
class LLUtil
{
// This function creates a linked list
// from a given array and returns head
public Node createLL(int[] arr)
{
Node head = new Node(arr[0]);
Node temp = head;
Node newNode = null;
for(int i = 1; i < arr.Length; i++)
{
newNode = new Node(arr[i]);
temp.next = newNode;
temp = temp.next;
}
return head;
}
// This function prints given linked list
public void printLL(Node head)
{
while (head != null)
{
Console.Write(head.data + " ");
head = head.next;
}
Console.WriteLine();
}
}
class GFG{
// Driver Code
public static void Main(string[] args)
{
int[] arr = { 12, 15, 10, 11, 5, 6, 2, 3 };
LLUtil llu = new LLUtil();
Node head = llu.createLL(arr);
Console.WriteLine("Given Linked List");
llu.printLL(head);
deleteNodesOnRightSide(head);
Console.WriteLine("Modified Linked List");
llu.printLL(head);
}
// Main function
public static void deleteNodesOnRightSide(Node head)
{
Node temp = head;
while (temp != null && temp.next != null)
{
// Copying next node data into current node
// i.e. we are indirectly deleting current node
if (temp.data < temp.next.data)
{
temp.data = temp.next.data;
temp.next = temp.next.next;
}
else
{
// Move to the next node
temp = temp.next;
}
}
}
}
// This code is contributed by rutvik_56Javascript
输出
Given Linked List
12 15 10 11 5 6 2 3
Modified Linked List
15 11 6 3方法三：
另一种更简单的方法是从头开始遍历链表，当当前节点<下一个节点时删除该节点。要删除当前节点，请遵循此方法。
让我们假设您必须删除当前节点 X
1.将下一个节点的数据复制到X中即X.data = X.next.data
2、复制next节点的下一个地址即X.next = X.next.next；
仅当当前节点 > 下一个节点时才在列表中向前移动。
Java
// Java program for above approach
import java.io.*;
// This class represents a single node
// in a linked list
class Node {
int data;
Node next;
public Node(int data){
this.data = data;
this.next = null;
}
}
//This is a utility class for linked list
class LLUtil{
// This function creates a linked list from a
// given array and returns head
public Node createLL(int[] arr){
Node head = new Node(arr[0]);
Node temp = head;
Node newNode = null;
for(int i = 1; i < arr.length; i++){
newNode = new Node(arr[i]);
temp.next = newNode;
temp = temp.next;
}
return head;
}
//This function prints given linked list
public void printLL(Node head){
while(head != null){
System.out.print(head.data + " ");
head = head.next;
}
System.out.println();
}
}
class GFG {
public static void main (String[] args) {
int[] arr = {12,15,10,11,5,6,2,3};
LLUtil llu = new LLUtil();
Node head = llu.createLL(arr);
System.out.println("Given Linked List");
llu.printLL(head);
head = deleteNodesOnRightSide(head);
System.out.println("Modified Linked List");
llu.printLL(head);
}
//Main function
public static Node deleteNodesOnRightSide(Node head){
if(head == null || head.next == null) return head;
Node nextNode = deleteNodesOnRightSide(head.next);
if(nextNode.data > head.data) return nextNode;
head.next = nextNode;
return head;
}
}
C＃
// C# program for above approach
using System;
// This class represents a single node
// in a linked list
class Node
{
public int data;
public Node next;
public Node(int data)
{
this.data = data;
this.next = null;
}
}
// This is a utility class for linked list
class LLUtil
{
// This function creates a linked list
// from a given array and returns head
public Node createLL(int[] arr)
{
Node head = new Node(arr[0]);
Node temp = head;
Node newNode = null;
for(int i = 1; i < arr.Length; i++)
{
newNode = new Node(arr[i]);
temp.next = newNode;
temp = temp.next;
}
return head;
}
// This function prints given linked list
public void printLL(Node head)
{
while (head != null)
{
Console.Write(head.data + " ");
head = head.next;
}
Console.WriteLine();
}
}
class GFG{
// Driver Code
public static void Main(string[] args)
{
int[] arr = { 12, 15, 10, 11, 5, 6, 2, 3 };
LLUtil llu = new LLUtil();
Node head = llu.createLL(arr);
Console.WriteLine("Given Linked List");
llu.printLL(head);
deleteNodesOnRightSide(head);
Console.WriteLine("Modified Linked List");
llu.printLL(head);
}
// Main function
public static void deleteNodesOnRightSide(Node head)
{
Node temp = head;
while (temp != null && temp.next != null)
{
// Copying next node data into current node
// i.e. we are indirectly deleting current node
if (temp.data < temp.next.data)
{
temp.data = temp.next.data;
temp.next = temp.next.next;
}
else
{
// Move to the next node
temp = temp.next;
}
}
}
}
// This code is contributed by rutvik_56
Javascript
输出
Given Linked List
12 15 10 11 5 6 2 3
Modified Linked List
15 11 6 3来源：
https://www.geeksforgeeks.org/forum/topic/amazon-interview-question-for-software-engineerdeveloper-about-linked-lists-6
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