查找链表的长度（迭代和递归）
原文：https://www.geeksforgeeks.org/find-length-of-a-linked-list-iterative-and-recursive/
编写一个函数以计算给定单链表中的节点数。
例如，对于链表1 -> 3 -> 1 -> 2 -> 1，该函数应返回 5。
迭代解决方案
1) Initialize count as 0
2) Initialize a node pointer, current = head.
3) Do following while current is not NULL
a) current = current -> next
b) count++;
4) Return count
以下是上述算法的实现，以找到节点数。
C++
// Iterative C++ program to find length
// or count of nodes in a linked list
#include <bits/stdc++.h>
using namespace std;
/* Link list node */
class Node
{
public:
int data;
Node* next;
};
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the 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;
}
/* Counts no. of nodes in linked list */
int getCount(Node* head)
{
int count = 0; // Initialize count
Node* current = head; // Initialize current
while (current != NULL)
{
count++;
current = current->next;
}
return count;
}
/* Driver program to test count function*/
int main()
{
/* Start with the empty list */
Node* head = NULL;
/* Use push() to construct below list
1->2->1->3->1 */
push(&head, 1);
push(&head, 3);
push(&head, 1);
push(&head, 2);
push(&head, 1);
/* Check the count function */
cout<<"count of nodes is "<< getCount(head);
return 0;
}
// This is code is contributed by rathbhupendra
C
// Iterative C program to find length or count of nodes in a linked list
#include<stdio.h>
#include<stdlib.h>
/* Link list node */
struct Node
{
int data;
struct Node* next;
};
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the 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;
}
/* Counts no. of nodes in linked list */
int getCount(struct Node* head)
{
int count = 0; // Initialize count
struct Node* current = head; // Initialize current
while (current != NULL)
{
count++;
current = current->next;
}
return count;
}
/* Driver program to test count function*/
int main()
{
/* Start with the empty list */
struct Node* head = NULL;
/* Use push() to construct below list
1->2->1->3->1 */
push(&head, 1);
push(&head, 3);
push(&head, 1);
push(&head, 2);
push(&head, 1);
/* Check the count function */
printf("count of nodes is %d", getCount(head));
return 0;
}
Java
// Java program to count number of nodes in a linked list
/* Linked list Node*/
class Node
{
int data;
Node next;
Node(int d) { data = d; next = null; }
}
// Linked List class
class LinkedList
{
Node head; // head of list
/* 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;
}
/* Returns count of nodes in linked list */
public int getCount()
{
Node temp = head;
int count = 0;
while (temp != null)
{
count++;
temp = temp.next;
}
return count;
}
/* Driver program to test above functions. Ideally
this function should be in a separate user class.
It is kept here to keep code compact */
public static void main(String[] args)
{
/* Start with the empty list */
LinkedList llist = new LinkedList();
llist.push(1);
llist.push(3);
llist.push(1);
llist.push(2);
llist.push(1);
System.out.println("Count of nodes is " +
llist.getCount());
}
}
Python
# A complete working Python program to find length of a
# Linked List iteratively
# Node class
class Node:
# Function to initialise the node object
def __init__(self, data):
self.data = data # Assign data
self.next = None # Initialize next as null
# Linked List class contains a Node object
class LinkedList:
# Function to initialize head
def __init__(self):
self.head = None
# This function is in LinkedList class. It inserts
# a new node at the beginning of Linked List.
def push(self, new_data):
# 1 & 2: Allocate the Node &
# Put in the data
new_node = Node(new_data)
# 3\. Make next of new Node as head
new_node.next = self.head
# 4\. Move the head to point to new Node
self.head = new_node
# This function counts number of nodes in Linked List
# iteratively, given 'node' as starting node.
def getCount(self):
temp = self.head # Initialise temp
count = 0 # Initialise count
# Loop while end of linked list is not reached
while (temp):
count += 1
temp = temp.next
return count
# Code execution starts here
if __name__=='__main__':
llist = LinkedList()
llist.push(1)
llist.push(3)
llist.push(1)
llist.push(2)
llist.push(1)
print ("Count of nodes is :",llist.getCount())
C
// C# program to count number
// of nodes in a linked list
using System;
/* Linked list Node*/
public class Node
{
public int data;
public Node next;
public Node(int d)
{
data = d; next = null;
}
}
// Linked List class
public class LinkedList
{
Node head; // head of list
/* 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;
}
/* Returns count of nodes in linked list */
public int getCount()
{
Node temp = head;
int count = 0;
while (temp != null)
{
count++;
temp = temp.next;
}
return count;
}
/* Driver program to test above functions. Ideally
this function should be in a separate user class.
It is kept here to keep code compact */
public static void Main()
{
/* Start with the empty list */
LinkedList llist = new LinkedList();
llist.push(1);
llist.push(3);
llist.push(1);
llist.push(2);
llist.push(1);
Console.WriteLine("Count of nodes is " +
llist.getCount());
}
}
/* This code contributed by PrinciRaj1992 */
输出：
count of nodes is 5
递归解决方案
int getCount(head)
1) If head is NULL, return 0.
2) Else return 1 + getCount(head->next)
以下是上述算法的实现，以找到节点数。
C/C++
// Recursive C program to find length or count of nodes in a linked list
#include<stdio.h>
#include<stdlib.h>
/* Link list node */
struct Node
{
int data;
struct Node* next;
};
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the 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;
}
/* Counts the no. of occurrences of a node
(search_for) in a linked list (head)*/
int getCount(struct Node* head)
{
// Base case
if (head == NULL)
return 0;
// count is 1 + count of remaining list
return 1 + getCount(head->next);
}
/* Driver program to test count function*/
int main()
{
/* Start with the empty list */
struct Node* head = NULL;
/* Use push() to construct below list
1->2->1->3->1 */
push(&head, 1);
push(&head, 3);
push(&head, 1);
push(&head, 2);
push(&head, 1);
/* Check the count function */
printf("count of nodes is %d", getCount(head));
return 0;
}
Java
// Recursive Java program to count number of nodes in
// a linked list
/* Linked list Node*/
class Node
{
int data;
Node next;
Node(int d) { data = d; next = null; }
}
// Linked List class
class LinkedList
{
Node head; // head of list
/* 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;
}
/* Returns count of nodes in linked list */
public int getCountRec(Node node)
{
// Base case
if (node == null)
return 0;
// Count is this node plus rest of the list
return 1 + getCountRec(node.next);
}
/* Wrapper over getCountRec() */
public int getCount()
{
return getCountRec(head);
}
/* Driver program to test above functions. Ideally
this function should be in a separate user class.
It is kept here to keep code compact */
public static void main(String[] args)
{
/* Start with the empty list */
LinkedList llist = new LinkedList();
llist.push(1);
llist.push(3);
llist.push(1);
llist.push(2);
llist.push(1);
System.out.println("Count of nodes is " +
llist.getCount());
}
}
Python
# A complete working Python program to find length of a
# Linked List recursively
# Node class
class Node:
# Function to initialise the node object
def __init__(self, data):
self.data = data # Assign data
self.next = None # Initialize next as null
# Linked List class contains a Node object
class LinkedList:
# Function to initialize head
def __init__(self):
self.head = None
# This function is in LinkedList class. It inserts
# a new node at the beginning of Linked List.
def push(self, new_data):
# 1 & 2: Allocate the Node &
# Put in the data
new_node = Node(new_data)
# 3\. Make next of new Node as head
new_node.next = self.head
# 4\. Move the head to point to new Node
self.head = new_node
# This function counts number of nodes in Linked List
# recursively, given 'node' as starting node.
def getCountRec(self, node):
if (not node): # Base case
return 0
else:
return 1 + self.getCountRec(node.next)
# A wrapper over getCountRec()
def getCount(self):
return self.getCountRec(self.head)
# Code execution starts here
if __name__=='__main__':
llist = LinkedList()
llist.push(1)
llist.push(3)
llist.push(1)
llist.push(2)
llist.push(1)
print 'Count of nodes is :',llist.getCount()
C
// Recursive C# program to count number of nodes in
// a linked list
using System;
/* Linked list Node*/
public class Node
{
public int data;
public Node next;
public Node(int d)
{
data = d; next = null;
}
}
// Linked List class
public class LinkedList
{
Node head; // head of list
/* 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;
}
/* Returns count of nodes in linked list */
public int getCountRec(Node node)
{
// Base case
if (node == null)
return 0;
// Count is this node plus rest of the list
return 1 + getCountRec(node.next);
}
/* Wrapper over getCountRec() */
public int getCount()
{
return getCountRec(head);
}
/* Driver program to test above functions. Ideally
this function should be in a separate user class.
It is kept here to keep code compact */
public static void Main(String[] args)
{
/* Start with the empty list */
LinkedList llist = new LinkedList();
llist.push(1);
llist.push(3);
llist.push(1);
llist.push(2);
llist.push(1);
Console.WriteLine("Count of nodes is " +
llist.getCount());
}
}
// This code is contributed 29AjayKumar
输出：
count of nodes is 5
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