在从末尾开始的第 n 个节点之后插入一个节点

在从末尾算起的第 n 个节点之后插入一个节点

在给定的单向链表中从末尾开始的第 n 个节点之后插入一个节点x 。保证列表包含从末尾开始的第 n 个节点。还有 1 <= n。

例子：

Input : list: 1->3->4->5
        n = 4, x = 2
Output : 1->2->3->4->5
4th node from the end is 1 and
insertion has been done after this node.

Input : list: 10->8->3->12->5->18
        n = 2, x = 11
Output : 10->8->3->12->5->11->18

方法一（使用列表长度）：
求链表的长度，即链表中的节点数。让它成为len 。现在从头开始遍历从第 1 个节点到第(len-n+1) 个节点的列表，并在该节点之后插入新节点。此方法需要对列表进行两次遍历。

C++

// C++ implementation to insert a node after
// the n-th node from the end
#include 
using namespace std;
 
// structure of a node
struct Node {
    int data;
    Node* next;
};
 
// function to get a new node
Node* getNode(int data)
{
    // allocate memory for the node
    Node* newNode = (Node*)malloc(sizeof(Node));
 
    // put in the data
    newNode->data = data;
    newNode->next = NULL;
    return newNode;
}
 
// function to insert a node after the
// nth node from the end
void insertAfterNthNode(Node* head, int n, int x)
{
    // if list is empty
    if (head == NULL)
        return;
 
    // get a new node for the value 'x'
    Node* newNode = getNode(x);
    Node* ptr = head;
    int len = 0, i;
 
    // find length of the list, i.e, the
    // number of nodes in the list
    while (ptr != NULL) {
        len++;
        ptr = ptr->next;
    }
 
    // traverse up to the nth node from the end
    ptr = head;
    for (i = 1; i <= (len - n); i++)
        ptr = ptr->next;
 
    // insert the 'newNode' by making the
    // necessary adjustment in the links
    newNode->next = ptr->next;
    ptr->next = newNode;
}
 
// function to print the list
void printList(Node* head)
{
    while (head != NULL) {
        cout << head->data << " ";
        head = head->next;
    }
}
 
// Driver program to test above
int main()
{
    // Creating list 1->3->4->5
    Node* head = getNode(1);
    head->next = getNode(3);
    head->next->next = getNode(4);
    head->next->next->next = getNode(5);
 
    int n = 4, x = 2;
 
    cout << "Original Linked List: ";
    printList(head);
 
    insertAfterNthNode(head, n, x);
 
    cout << "\nLinked List After Insertion: ";
    printList(head);
 
    return 0;
}

Java

// Java implementation to insert a node after
// the n-th node from the end
class GfG
{
 
// structure of a node
static class Node
{
    int data;
    Node next;
}
 
// function to get a new node
static Node getNode(int data)
{
    // allocate memory for the node
    Node newNode = new Node();
 
    // put in the data
    newNode.data = data;
    newNode.next = null;
    return newNode;
}
 
// function to insert a node after the
// nth node from the end
static void insertAfterNthNode(Node head, int n, int x)
{
    // if list is empty
    if (head == null)
        return;
 
    // get a new node for the value 'x'
    Node newNode = getNode(x);
    Node ptr = head;
    int len = 0, i;
 
    // find length of the list, i.e, the
    // number of nodes in the list
    while (ptr != null)
    {
        len++;
        ptr = ptr.next;
    }
 
    // traverse up to the nth node from the end
    ptr = head;
    for (i = 1; i <= (len - n); i++)
        ptr = ptr.next;
 
    // insert the 'newNode' by making the
    // necessary adjustment in the links
    newNode.next = ptr.next;
    ptr.next = newNode;
}
 
// function to print the list
static void printList(Node head)
{
    while (head != null)
    {
        System.out.print(head.data + " ");
        head = head.next;
    }
}
 
// Driver code
public static void main(String[] args)
{
    // Creating list 1->3->4->5
    Node head = getNode(1);
    head.next = getNode(3);
    head.next.next = getNode(4);
    head.next.next.next = getNode(5);
 
    int n = 4, x = 2;
 
    System.out.print("Original Linked List: ");
    printList(head);
 
    insertAfterNthNode(head, n, x);
    System.out.println();
    System.out.print("Linked List After Insertion: ");
    printList(head);
}
}
 
// This code is contributed by prerna saini

Python3

# Python implementation to insert a node after
# the n-th node from the end
 
# Linked List node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None
 
# function to get a new node
def getNode(data) :
 
    # allocate memory for the node
    newNode = Node(0)
 
    # put in the data
    newNode.data = data
    newNode.next = None
    return newNode
 
# function to insert a node after the
# nth node from the end
def insertAfterNthNode(head, n, x) :
 
    # if list is empty
    if (head == None) :
        return
 
    # get a new node for the value 'x'
    newNode = getNode(x)
    ptr = head
    len = 0
    i = 0
 
    # find length of the list, i.e, the
    # number of nodes in the list
    while (ptr != None) :
     
        len = len + 1
        ptr = ptr.next
     
    # traverse up to the nth node from the end
    ptr = head
    i = 1
    while ( i <= (len - n) ) :
        ptr = ptr.next
        i = i + 1
 
    # insert the 'newNode' by making the
    # necessary adjustment in the links
    newNode.next = ptr.next
    ptr.next = newNode
 
# function to print the list
def printList( head) :
 
    while (head != None):
     
        print(head.data ,end = " ")
        head = head.next
     
# Driver code
 
# Creating list 1->3->4->5
head = getNode(1)
head.next = getNode(3)
head.next.next = getNode(4)
head.next.next.next = getNode(5)
 
n = 4
x = 2
 
print("Original Linked List: ")
printList(head)
 
insertAfterNthNode(head, n, x)
print()
print("Linked List After Insertion: ")
printList(head)
 
# This code is contributed by Arnab Kundu

C#

// C# implementation to insert a node after
// the n-th node from the end
using System;
 
class GfG
{
 
// structure of a node
public class Node
{
    public int data;
    public Node next;
}
 
// function to get a new node
static Node getNode(int data)
{
    // allocate memory for the node
    Node newNode = new Node();
 
    // put in the data
    newNode.data = data;
    newNode.next = null;
    return newNode;
}
 
// function to insert a node after the
// nth node from the end
static void insertAfterNthNode(Node head, int n, int x)
{
    // if list is empty
    if (head == null)
        return;
 
    // get a new node for the value 'x'
    Node newNode = getNode(x);
    Node ptr = head;
    int len = 0, i;
 
    // find length of the list, i.e, the
    // number of nodes in the list
    while (ptr != null)
    {
        len++;
        ptr = ptr.next;
    }
 
    // traverse up to the nth node from the end
    ptr = head;
    for (i = 1; i <= (len - n); i++)
        ptr = ptr.next;
 
    // insert the 'newNode' by making the
    // necessary adjustment in the links
    newNode.next = ptr.next;
    ptr.next = newNode;
}
 
// function to print the list
static void printList(Node head)
{
    while (head != null)
    {
        Console.Write(head.data + " ");
        head = head.next;
    }
}
 
// Driver code
public static void Main(String[] args)
{
    // Creating list 1->3->4->5
    Node head = getNode(1);
    head.next = getNode(3);
    head.next.next = getNode(4);
    head.next.next.next = getNode(5);
 
    int n = 4, x = 2;
 
    Console.Write("Original Linked List: ");
    printList(head);
 
    insertAfterNthNode(head, n, x);
    Console.WriteLine();
    Console.Write("Linked List After Insertion: ");
    printList(head);
}
}
 
// This code has been contributed by 29AjayKumar

Javascript

 
// JavaScript implementation to
// insert a node after
// the n-th node from the end
 
    // structure of a node
     class Node {
            constructor() {
                this.data = 0;
                this.next = null;
            }
        }
 
    // function to get a new node
    function getNode(data) {
        // allocate memory for the node
var newNode = new Node();
 
        // put in the data
        newNode.data = data;
        newNode.next = null;
        return newNode;
    }
 
    // function to insert a node after the
    // nth node from the end
    function insertAfterNthNode(head , n , x) {
        // if list is empty
        if (head == null)
            return;
 
        // get a new node for the value 'x'
var newNode = getNode(x);
var ptr = head;
        var len = 0, i;
 
        // find length of the list, i.e, the
        // number of nodes in the list
        while (ptr != null) {
            len++;
            ptr = ptr.next;
        }
 
        // traverse up to the nth node from the end
        ptr = head;
        for (i = 1; i <= (len - n); i++)
            ptr = ptr.next;
 
        // insert the 'newNode' by making the
        // necessary adjustment in the links
        newNode.next = ptr.next;
        ptr.next = newNode;
    }
 
    // function to print the list
    function printList(head) {
        while (head != null) {
            document.write(head.data + " ");
            head = head.next;
        }
    }
 
    // Driver code
     
        // Creating list 1->3->4->5
var head = getNode(1);
        head.next = getNode(3);
        head.next.next = getNode(4);
        head.next.next.next = getNode(5);
 
        var n = 4, x = 2;
 
        document.write("Original Linked List: ");
        printList(head);
 
        insertAfterNthNode(head, n, x);
        document.write();
        document.write("<br/>Linked List After Insertion: ");
        printList(head);
 
// This code contributed by gauravrajput1
 

输出：

Original Linked List: 1 3 4 5
Linked List After Insertion: 1 2 3 4 5

时间复杂度： O(n)，其中n是列表中的节点数。

方法二（单次遍历）：
该方法使用两个指针，一个是slow_ptr ，另一个是fast_ptr 。首先将fast_ptr 从头移到第n 个节点。使slow_ptr指向列表的第一个节点。现在，同时移动两个指针，直到fast_ptr指向最后一个节点。此时， slow_ptr将指向末尾的第 n 个节点。在此节点之后插入新节点。此方法需要单次遍历列表。

C++

// C++ implementation to insert a node after the
// nth node from the end
#include 
 
using namespace std;
 
// structure of a node
struct Node {
    int data;
    Node* next;
};
 
// function to get a new node
Node* getNode(int data)
{
    // allocate memory for the node
    Node* newNode = (Node*)malloc(sizeof(Node));
 
    // put in the data
    newNode->data = data;
    newNode->next = NULL;
    return newNode;
}
 
// function to insert a node after the
// nth node from the end
void insertAfterNthNode(Node* head, int n, int x)
{
    // if list is empty
    if (head == NULL)
        return;
 
    // get a new node for the value 'x'
    Node* newNode = getNode(x);
 
    // Initializing the slow and fast pointers
    Node* slow_ptr = head;
    Node* fast_ptr = head;
 
    // move 'fast_ptr' to point to the nth node
    // from the beginning
    for (int i = 1; i <= n - 1; i++)
        fast_ptr = fast_ptr->next;
 
    // iterate until 'fast_ptr' points to the
    // last node
    while (fast_ptr->next != NULL) {
 
        // move both the pointers to the
        // respective next nodes
        slow_ptr = slow_ptr->next;
        fast_ptr = fast_ptr->next;
    }
 
    // insert the 'newNode' by making the
    // necessary adjustment in the links
    newNode->next = slow_ptr->next;
    slow_ptr->next = newNode;
}
 
// function to print the list
void printList(Node* head)
{
    while (head != NULL) {
        cout << head->data << " ";
        head = head->next;
    }
}
 
// Driver program to test above
int main()
{
    // Creating list 1->3->4->5
    Node* head = getNode(1);
    head->next = getNode(3);
    head->next->next = getNode(4);
    head->next->next->next = getNode(5);
 
    int n = 4, x = 2;
 
    cout << "Original Linked List: ";
    printList(head);
 
    insertAfterNthNode(head, n, x);
 
    cout << "\nLinked List After Insertion: ";
    printList(head);
 
    return 0;
}

Java

// Java implementation to
// insert a node after the
// nth node from the end
class GfG
{
 
// structure of a node
static class Node
{
    int data;
    Node next;
}
 
// function to get a new node
static Node getNode(int data)
{
    // allocate memory for the node
    Node newNode = new Node();
 
    // put in the data
    newNode.data = data;
    newNode.next = null;
    return newNode;
}
 
// function to insert a node after
// the nth node from the end
static void insertAfterNthNode(Node head,
                            int n, int x)
{
    // if list is empty
    if (head == null)
        return;
 
    // get a new node for the value 'x'
    Node newNode = getNode(x);
 
    // Initializing the slow
    // and fast pointers
    Node slow_ptr = head;
    Node fast_ptr = head;
 
    // move 'fast_ptr' to point to the
    // nth node from the beginning
    for (int i = 1; i <= n - 1; i++)
        fast_ptr = fast_ptr.next;
 
    // iterate until 'fast_ptr' points 
    // to the last node
    while (fast_ptr.next != null)
    {
 
        // move both the pointers to the
        // respective next nodes
        slow_ptr = slow_ptr.next;
        fast_ptr = fast_ptr.next;
    }
 
    // insert the 'newNode' by making the
    // necessary adjustment in the links
    newNode.next = slow_ptr.next;
    slow_ptr.next = newNode;
}
 
// function to print the list
static void printList(Node head)
{
    while (head != null)
    {
        System.out.print(head.data + " ");
        head = head.next;
    }
}
 
// Driver code
public static void main(String[] args)
{
    // Creating list 1->3->4->5
    Node head = getNode(1);
    head.next = getNode(3);
    head.next.next = getNode(4);
    head.next.next.next = getNode(5);
 
    int n = 4, x = 2;
    System.out.println("Original Linked List: ");
    printList(head);
 
    insertAfterNthNode(head, n, x);
    System.out.println();
    System.out.println("Linked List After Insertion: ");
    printList(head);
}
}
 
// This code is contributed by
// Prerna Saini.

蟒蛇3

# Python3 implementation to insert a
# node after the nth node from the end
  
# Structure of a node
class Node:
     
    def __init__(self, data):
         
        self.data = data
        self.next = None
     
# Function to get a new node
def getNode(data):
     
    # Allocate memory for the node
    newNode = Node(data)
    return newNode
 
# Function to insert a node after the
# nth node from the end
def insertAfterNthNode(head, n, x):
 
    # If list is empty
    if (head == None):
        return
  
    # Get a new node for the value 'x'
    newNode = getNode(x)
  
    # Initializing the slow and fast pointers
    slow_ptr = head
    fast_ptr = head
  
    # Move 'fast_ptr' to point to the nth
    # node from the beginning
    for i in range(1, n):
        fast_ptr = fast_ptr.next
  
    # Iterate until 'fast_ptr' points to the
    # last node
    while (fast_ptr.next != None):
  
        # Move both the pointers to the
        # respective next nodes
        slow_ptr = slow_ptr.next
        fast_ptr = fast_ptr.next
 
    # Insert the 'newNode' by making the
    # necessary adjustment in the links
    newNode.next = slow_ptr.next
    slow_ptr.next = newNode
 
# Function to print the list
def printList(head):
 
    while (head != None):
        print(head.data, end = ' ')
        head = head.next
     
# Driver code
if __name__=='__main__':
     
    # Creating list 1.3.4.5
    head = getNode(1)
    head.next = getNode(3)
    head.next.next = getNode(4)
    head.next.next.next = getNode(5)
  
    n = 4
    x = 2
  
    print("Original Linked List: ", end = '')
    printList(head)
  
    insertAfterNthNode(head, n, x)
  
    print("\nLinked List After Insertion: ", end = '')
    printList(head)
  
# This code is contributed by rutvik_56

C＃

// C# implementation to
// insert a node after the
// nth node from the end
using System;
 
class GfG
{
 
    // structure of a node
    public class Node
    {
        public int data;
        public Node next;
    }
 
    // function to get a new node
    static Node getNode(int data)
    {
        // allocate memory for the node
        Node newNode = new Node();
 
        // put in the data
        newNode.data = data;
        newNode.next = null;
        return newNode;
    }
 
    // function to insert a node after
    // the nth node from the end
    static void insertAfterNthNode(Node head,
                                int n, int x)
    {
        // if list is empty
        if (head == null)
            return;
 
        // get a new node for the value 'x'
        Node newNode = getNode(x);
 
        // Initializing the slow
        // and fast pointers
        Node slow_ptr = head;
        Node fast_ptr = head;
 
        // move 'fast_ptr' to point to the
        // nth node from the beginning
        for (int i = 1; i <= n - 1; i++)
            fast_ptr = fast_ptr.next;
 
        // iterate until 'fast_ptr' points
        // to the last node
        while (fast_ptr.next != null)
        {
 
            // move both the pointers to the
            // respective next nodes
            slow_ptr = slow_ptr.next;
            fast_ptr = fast_ptr.next;
        }
 
        // insert the 'newNode' by making the
        // necessary adjustment in the links
        newNode.next = slow_ptr.next;
        slow_ptr.next = newNode;
    }
 
    // function to print the list
    static void printList(Node head)
    {
        while (head != null)
        {
            Console.Write(head.data + " ");
            head = head.next;
        }
    }
 
    // Driver code
    public static void Main()
    {
        // Creating list 1->3->4->5
        Node head = getNode(1);
        head.next = getNode(3);
        head.next.next = getNode(4);
        head.next.next.next = getNode(5);
 
        int n = 4, x = 2;
        Console.WriteLine("Original Linked List: ");
        printList(head);
 
        insertAfterNthNode(head, n, x);
        Console.WriteLine();
        Console.WriteLine("Linked List After Insertion: ");
        printList(head);
    }
}
 
/* This code contributed by PrinciRaj1992 */

Javascript

 
      // JavaScript implementation to
      // insert a node after the
      // nth node from the end
      // structure of a node
      class Node {
        constructor() {
          this.data = 0;
          this.next = null;
        }
      }
 
      // function to get a new node
      function getNode(data) {
        // allocate memory for the node
        var newNode = new Node();
 
        // put in the data
        newNode.data = data;
        newNode.next = null;
        return newNode;
      }
 
      // function to insert a node after
      // the nth node from the end
      function insertAfterNthNode(head, n, x) {
        // if list is empty
        if (head == null) return;
 
        // get a new node for the value 'x'
        var newNode = getNode(x);
 
        // Initializing the slow
        // and fast pointers
        var slow_ptr = head;
        var fast_ptr = head;
 
        // move 'fast_ptr' to point to the
        // nth node from the beginning
        for (var i = 1; i <= n - 1; i++)
        fast_ptr = fast_ptr.next;
 
        // iterate until 'fast_ptr' points
        // to the last node
        while (fast_ptr.next != null) {
          // move both the pointers to the
          // respective next nodes
          slow_ptr = slow_ptr.next;
          fast_ptr = fast_ptr.next;
        }
 
        // insert the 'newNode' by making the
        // necessary adjustment in the links
        newNode.next = slow_ptr.next;
        slow_ptr.next = newNode;
      }
 
      // function to print the list
      function printList(head) {
        while (head != null) {
          document.write(head.data + " ");
          head = head.next;
        }
      }
 
      // Driver code
      // Creating list 1->3->4->5
      var head = getNode(1);
      head.next = getNode(3);
      head.next.next = getNode(4);
      head.next.next.next = getNode(5);
 
      var n = 4,
        x = 2;
      document.write("Original Linked List: ");
      printList(head);
 
      insertAfterNthNode(head, n, x);
      document.write("<br>");
      document.write("Linked List After Insertion:");
      printList(head);
       

输出：

Original Linked List: 1 3 4 5
Linked List After Insertion: 1 2 3 4 5

时间复杂度： O(n)，其中n是列表中的节点数。

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