Python Program to Count the Occurrences of Elements in a Linked List without Recursion

This is a Python program to count the number of occurrences of an element in a linked list without using recursion.

Problem Description

The program prompts the user for a key and displays the number of times the key occurs in the linked list.

Problem Solution

1. Create a class Node.
2. Create a class LinkedList.
3. Define methods append and display inside the class LinkedList to append data and display the linked list respectively.
4. Define method count.
5. count uses a loop and a variable to count the number of occurrences of a key.
6. Create an instance of LinkedList, append data to it and display the list.
7. Prompt the user for a key and display the number of times it occurs by calling the method count.

Program/Source Code

Here is the source code of a Python program to count the number of occurrences of an element in a linked list without using recursion. The program output is shown below.

class Node:
    def __init__(self, data):
       self.data = data
       self.next = None
 
class LinkedList:
    def __init__(self):
        self.head = None
        self.last_node = None
 
    def append(self, data):
        if self.last_node is None:
            self.head = Node(data)
            self.last_node = self.head
        else:
            self.last_node.next = Node(data)
            self.last_node = self.last_node.next
 
    def display(self):
        current = self.head
        while current:
            print(current.data, end = ' ')
            current = current.next
 
    def count(self, key):
        current = self.head
 
        count = 0
        while current:
            if current.data == key:
                count = count + 1
            current = current.next
 
        return count
 
a_llist = LinkedList()
for data in [5, 1, 3, 5, 5, 15, 4, 9, 2]:
    a_llist.append(data)
print('The linked list: ', end = '')
a_llist.display()
print()
 
key = int(input('Enter data item: '))
count = a_llist.count(key)
print('{0} occurs {1} time(s) in the list.'.format(key, count))
Program Explanation

1. An instance of LinkedList is created.
2. Some elements are appended to the list.
3. The linked list is displayed.
4. The user is prompted for a key to enter.
5. count counts the number of times the key occurs in the list.
6. The count determined is then displayed.

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Runtime Test Cases
Case 1:
The linked list: 5 1 3 5 5 15 4 9 2 
Enter data item: 5
5 occurs 3 time(s) in the list.
 
Case 2:
The linked list: 5 1 3 5 5 15 4 9 2 
Enter data item: 3
3 occurs 1 time(s) in the list.
 
Case 3:
The linked list: 5 1 3 5 5 15 4 9 2 
Enter data item: 7
7 occurs 0 time(s) in the list.

Sanfoundry Global Education & Learning Series – Python Programs.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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