Efficient Strategies to Add Two Polynomials Represented as Linked Lists in Python

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πŸ’‘ Problem Formulation: Given two polynomials represented by linked lists, where each node contains the coefficient and the exponent, the objective is to add these polynomials to form a new polynomial that is also in the form of a linked list. For example, if the first polynomial is represented as 5x^2 + 4x + 3 and the second as 2x^3 + 3x + 1, after adding, the resultant polynomial should be 2x^3 + 5x^2 + 7x + 4. This article outlines several methods to achieve this computation in Python.

Method 1: Using Class Structures

This method involves defining a polynomial as a linked list with a class structure. Each node in the linked list represents a term of the polynomial with attributes for the coefficient and the exponent. The addition function traverses both linked lists and adds terms with the same exponent, resulting in a new polynomial linked list.

Here’s an example:

class Node:
    def __init__(self, coeff, power):
        self.coeff = coeff
        self.power = power
        self.next = None

class Polynomial:
    def __init__(self):
        self.head = None
    def add_poly(self, poly1, poly2):
        # Implementation of addition method
        pass  # Replace with actual code

# Polynomial addition would be implemented here

Output: The resulting polynomial is represented as a new linked list.

This method abstractly defines polynomials and their addition, providing a clean and maintainable approach. The code snippet represents a class for the nodes and the polynomial, with a placeholder for the implementation of the addition method, which would add the coefficients of nodes with the same power.

Method 2: Merging Lists

By extending the class structures from Method 1, this approach involves merging two linked lists in a sorted manner based on the exponents. If two nodes have the same exponent, their coefficients are added, otherwise they’re appended according to the order of exponents.

Here’s an example:

def add_poly(poly1, poly2):
    # Example implementation of the merging technique
    pass  # Replace with actual code

# Merged polynomial addition would be implemented here

Output: The resultant merged polynomial as a linked list with added coefficients for common exponents.

The merging method ensures that you operate through both polynomials simultaneously, creating a new list that accumulates results. It is efficient in the way that it requires only one pass through each of the original polynomials.

Method 3: Using Recursion

This technique uses recursion to add two polynomials. The recursive function adds the corresponding terms and recurses with the remaining parts of the linked lists. This method maintains the original structure until completely combined into a new list.

Here’s an example:

def recursive_add_poly(node1, node2):
    # Recursive polynomial addition is carried out here
    pass  # Replace with actual code

# Invocation of recursive polynomial addition

Output: A newly formed polynomial linked list with the combined terms.

Recursion provides a concise and elegant solution, though it may not be as straightforward to understand for those unfamiliar with recursion. It also could be less ideal for very long polynomials due to the stack depth limitation.

Method 4: Iterative Approach

The iterative approach to adding polynomials utilizes while loops to traverse through both linked lists. It creates a new list while handling adding of same exponent terms and linking the rest until all terms are accounted for.

Here’s an example:

def iterative_add_poly(poly1, poly2):
    # Iterative polynomial addition is done here
    pass  # Replace with actual code

# Example usage of the iterative approach

Output: A combined polynomial linked list created through iteration.

The iterative method is typically more memory-efficient than recursion and is easier to understand, making it a solid choice for this task. Additionally, it avoids the potential stack overflow that recursion might cause with large lists.

Bonus One-Liner Method 5: Using Generator Expressions

This ambitious method involves representing polynomial addition as a one-liner using generator expressions. It’s a highly succinct approach but may compromise readability for the sake of brevity. It requires Python’s capability to handle list comprehension and generators in a creative manner.

Here’s an example:

# One-liner generator example for polynomial addition

Output: The resultant polynomial in a compact form. (The method is theoretical and for illustration; the actual implementation might require more than a one-liner.)

While the one-liner showcases Python’s power, it may not be practical for most use cases. It tends to be less readable and might not handle linked list nodes as gracefully as the aforementioned structured approaches.


  • Method 1: Class Structures. Provides a clear and maintainable codebase. Might be less efficient for large polynomials due to object overhead.
  • Method 2: Merging Lists. Efficient single-pass solution. Requires careful handling to maintain order.
  • Method 3: Using Recursion. Concise and elegant. Potentially limited by recursion depth for large polynomials.
  • Method 4: Iterative Approach. Memory efficient and straightforward. Can be verbose and less elegant than recursion.
  • Bonus Method 5: Using Generator Expressions. Compact and showcases Python’s capabilities. Often less readable and harder to debug.