Python program to find the maximum and minimum value node from a doubly linked list

When it is required to find the maximum and minimum values from a doubly linked list, a Node class needs to be created. In this class, there are three attributes: the data that is present in the node, the access to the next node of the linked list, and the access to the previous node of the linked list.

A doubly linked list allows traversal in both directions, making it easy to find minimum and maximum values by iterating through all nodes once.

Implementation

Below is a complete implementation that creates a doubly linked list and finds the maximum and minimum values ?

class Node:
    def __init__(self, my_data):
        self.prev = None
        self.data = my_data
        self.next = None

class DoublyLinkedList:
    def __init__(self):
        self.head = None
        self.tail = None
    
    def add_data(self, my_data):
        new_node = Node(my_data)
        if self.head == None:
            self.head = self.tail = new_node
            self.head.prev = None
            self.tail.next = None
        else:
            self.tail.next = new_node
            new_node.prev = self.tail
            self.tail = new_node
            self.tail.next = None
    
    def min_node(self):
        curr = self.head
        if self.head == None:
            print("The list is empty")
            return None
        else:
            min_val = self.head.data
            while curr != None:
                if min_val > curr.data:
                    min_val = curr.data
                curr = curr.next
            return min_val
    
    def max_node(self):
        curr = self.head
        if self.head == None:
            print("The list is empty")
            return None
        else:
            max_val = self.head.data
            while curr != None:
                if curr.data > max_val:
                    max_val = curr.data
                curr = curr.next
            return max_val
    
    def print_it(self):
        curr = self.head
        if self.head == None:
            print("The list is empty")
            return
        print("The nodes in the doubly linked list are:")
        while curr != None:
            print(curr.data)
            curr = curr.next

# Create instance and test
my_instance = DoublyLinkedList()
print("Elements are being added to the doubly linked list")

my_instance.add_data(10)
my_instance.add_data(24)
my_instance.add_data(54)
my_instance.add_data(77)
my_instance.add_data(92)

my_instance.print_it()
print("The node with maximum value is:", my_instance.max_node())
print("The node with minimum value is:", my_instance.min_node())

Output

Elements are being added to the doubly linked list
The nodes in the doubly linked list are:
10
24
54
77
92
The node with maximum value is: 92
The node with minimum value is: 10

How It Works

The algorithm works by traversing the entire doubly linked list once for each operation:

• Node Class: Contains data and pointers to both previous and next nodes
• add_data(): Adds new nodes at the tail of the list
• min_node(): Traverses the list and keeps track of the minimum value found
• max_node(): Traverses the list and keeps track of the maximum value found
• print_it(): Displays all nodes in the list from head to tail

Key Features

• Time Complexity: O(n) for both min and max operations
• Space Complexity: O(1) additional space for the search operations
• Edge Case Handling: Returns None for empty lists
• Single Pass: Each operation requires only one traversal of the list

Conclusion

Finding minimum and maximum values in a doubly linked list requires a single traversal with O(n) time complexity. The doubly linked structure provides flexibility for bidirectional traversal, though only forward traversal is needed for min/max operations.