Python Program to Search an Element in Linked List without Recursion

This is a Python program to search for an element in a linked list without using recursion.

Problem Description

The program prompts the user for a key to search in a linked list and displays its index.

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 find_index to search for the key.
5. find_index uses a loop to iterate over the nodes of the linked list to search for the key.
6. Create an instance of LinkedList, append data to it and display the list.
7. Prompt the user for a key to search and search for it.

Program/Source Code

Here is the source code of a Python program to search for 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 is not None:
            print(current.data, end = ' ')
            current = current.next
 
    def find_index(self, key):
        current = self.head
 
        index = 0
        while current:
            if current.data == key:
                return index
            current = current.next
            index = index + 1
 
        return -1
 
a_llist = LinkedList()
for data in [4, -3, 1, 0, 9, 11]:
    a_llist.append(data)
print('The linked list: ', end = '')
a_llist.display()
print()
 
key = int(input('What data item would you like to search for? '))
index = a_llist.find_index(key)
if index == -1:
    print(str(key) + ' was not found.')
else:
    print(str(key) + ' is at index ' + str(index) + '.')

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 search.
5. find_index searches for the index. It returns -1 if the key is not found.
6. The index is displayed if found.

Runtime Test Cases

Case 1:
The linked list: 4 -3 1 0 9 11 
What data item would you like to search for? 9
9 is at index 4.
 
Case 2:
The linked list: 4 -3 1 0 9 11 
What data item would you like to search for? 11
11 is at index 5.
 
Case 3:
The linked list: 4 -3 1 0 9 11 
What data item would you like to search for? 3
3 was not found.

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