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.

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

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.

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))

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.

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.

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