Adding two polynomials using Linked List using map

Given two polynomial numbers represented by a linked list. Write a function to perform their algebraic sum. Examples:

Input: 1st number = 5x^2 + 4x^1 + 2x^0 2nd number = 5x^1 + 5x^0 Output: 5x^2 + 9x^1 + 7x^0

Approach: The implementation uses map data structure so that all coefficients of same power value are added together and kept in key-value pairs inside a map. Below is the implementation of the above approach: 

CPP

// C++ program for addition of two polynomials
// represented as linked lists
#include <bits/stdc++.h>
using namespace std;

// Structure of Node used
struct Node {

    // Coefficient of the polynomial
    int coeff;

    // Power of the polynomial
    int pow;
    Node* next;
};

// Function to create new node
void create_node(int x, int y, struct Node** temp)
{
    struct Node *r, *z;
    z = *temp;
    if (z == NULL) {
        r = (struct Node*)malloc(sizeof(struct Node));
        r->coeff = x;
        r->pow = y;
        *temp = r;
        r->next = (struct Node*)malloc(sizeof(struct Node));
        r = r->next;
        r->next = NULL;
    }
    else {
        r->coeff = x;
        r->pow = y;
        r->next = (struct Node*)malloc(sizeof(struct Node));
        r = r->next;
        r->next = NULL;
    }
}

// Display Linked list
void show(struct Node* node)
{
    if (node == NULL)
        return;
    while (node->next != NULL) {
        printf("%dx^%d", node->coeff, node->pow);
        node = node->next;
        if (node->next != NULL)
            printf(" + ");
    }
}

/* Function to print the required sum of a
polynomial p1 and p2 as specified in output */
void addPolynomial(Node* p1, Node* p2)
{
    map<int, int> mp;
    Node* temp1 = p1;
    Node* temp2 = p2;
    while (temp1 != NULL) {

        // Add coefficients of same power value
        // map contains (powervalue, coeff) pair
        mp[temp1->pow] += temp1->coeff;
        temp1 = temp1->next;
    }
    while (temp2 != NULL) {
        mp[temp2->pow] += temp2->coeff;
        temp2 = temp2->next;
    }

    // Started from the end because higher power should
    // come first and there should be "+" symbol in between
    // so iterate up to second element and print last out of
    // the loop.

    for (auto it = (mp.rbegin()); it != prev(mp.rend());
         ++it)
        cout << it->second << "x^" << it->first << " + ";
    cout << mp.begin()->second << "x^" << mp.begin()->first;
}

// Driver function
int main()
{
    struct Node *poly1 = NULL, *poly2 = NULL, *poly = NULL;

    // Create first list of 5x^2 + 4x^1 + 2x^0
    create_node(5, 2, &poly1);
    create_node(4, 1, &poly1);
    create_node(2, 0, &poly1);

    // Create second list of 5x^1 + 5x^0
    create_node(5, 1, &poly2);
    create_node(5, 0, &poly2);

    printf("1st Number: ");
    show(poly1);

    printf("\n2nd Number: ");
    show(poly2);

    poly = (struct Node*)malloc(sizeof(struct Node));

    printf("\nAdded polynomial: ");

    // Function add two polynomial numbers
    addPolynomial(poly1, poly2);

    return 0;
}

Java

// Java program for addition of two polynomials
// represented as linked lists
import java.util.*;

// Structure of Node used
class Node {

    // Coefficient of the polynomial
    int coeff;

    // Power of the polynomial
    int pow;
    Node next;

    Node(int coeff, int pow) {
        this.coeff = coeff;
        this.pow = pow;
        this.next = null;
    }
}

// Display Linked list
class LinkedList {

    Node head;

    // Function to create new node
    void create_node(int x, int y) {
        Node node = new Node(x, y);
        if (head == null) {
            head = node;
        }
        else {
            Node temp = head;
            while (temp.next != null) {
                temp = temp.next;
            }
            temp.next = node;
        }
    }

    void show() {
        Node node = head;
        while (node != null) {
            System.out.print(node.coeff + "x^" + node.pow);
            node = node.next;
            if (node != null) {
                System.out.print(" + ");
            }
        }
    }
}

class Main {

    // Function to print the required sum of a
    // polynomial p1 and p2 as specified in output
    static void addPolynomial(Node p1, Node p2) {
        Map<Integer, Integer> mp = new TreeMap<>(Collections.reverseOrder());
        Node temp1 = p1;
        Node temp2 = p2;
        while (temp1 != null) {

            // Add coefficients of same power value
            // map contains (powervalue, coeff) pair
            mp.put(temp1.pow, mp.getOrDefault(temp1.pow, 0) + temp1.coeff);
            temp1 = temp1.next;
        }
        while (temp2 != null) {
            mp.put(temp2.pow, mp.getOrDefault(temp2.pow, 0) + temp2.coeff);
            temp2 = temp2.next;
        }

        // Started from the end because higher power should
        // come first and there should be "+" symbol in between
        // so iterate up to second element and print last out of
        // the loop.
        boolean first = true;
        for (Map.Entry<Integer, Integer> entry : mp.entrySet()) {
            int pow = entry.getKey();
            int coeff = entry.getValue();
            if (first) {
                System.out.print(coeff + "x^" + pow);
                first = false;
            } else {
                System.out.print(" + " + coeff + "x^" + pow);
            }
        }
    }

    // Driver function
    public static void main(String[] args) {
        LinkedList poly1 = new LinkedList();
        LinkedList poly2 = new LinkedList();

        // Create first list of 5x^2 + 4x^1 + 2x^0
        poly1.create_node(5, 2);
        poly1.create_node(4, 1);
        poly1.create_node(2, 0);

        // Create second list of 5x^1 + 5x^0
        poly2.create_node(5, 1);
        poly2.create_node(5, 0);

        System.out.print("1st Number: ");
        poly1.show();

        System.out.print("\n2nd Number: ");
        poly2.show();

        System.out.print("\nAdded polynomial: ");

        // Function add two polynomial numbers
        addPolynomial(poly1.head, poly2.head);
    }
}
// This code is contributed by Prajwal Kandekar

Python3

# Python program for addition of two polynomials
# represented as linked lists

# Structure of Node used
class Node:
    # Coefficient of the polynomial
    def __init__(self, coeff, pow):
        self.coeff = coeff
        # Power of the polynomial
        self.pow = pow
        self.next = None

# Function to create new node
def create_node(x, y):
    r = Node(x, y)
    r.next = None
    return r

# Display Linked list
def show(node):
    if node is None:
        return
    while node.next is not None:
        print(f"{node.coeff}x^{node.pow}", end="")
        print(" + ", end="")
        node = node.next
        if node.next is not None:
            print(" ", end="")
    print(f"{node.coeff}x^{node.pow}")

# Function to print the required sum of a
# polynomial p1 and p2 as specified in output
def addPolynomial(p1, p2):
    mp = {}
    temp1 = p1
    temp2 = p2
    while temp1 is not None:
        # Add coefficients of same power value
        # map contains (powervalue, coeff) pair
        mp[temp1.pow] = mp.get(temp1.pow, 0) + temp1.coeff
        temp1 = temp1.next
    while temp2 is not None:
        mp[temp2.pow] = mp.get(temp2.pow, 0) + temp2.coeff
        temp2 = temp2.next

    # Started from the end because higher power should
    # come first and there should be "+" symbol in between
    # so iterate up to second element and print last out of
    # the loop.
    for power in sorted(mp.keys(), reverse=True):
        print(f"{mp[power]}x^{power}", end="")
        if power != sorted(mp.keys(), reverse=True)[-1]:
            print(" + ", end="")

# Driver function
if __name__ == "__main__":
    poly1 = None
    poly2 = None
    poly = None

    # Create first list of 5x^2 + 4x^1 + 2x^0
    poly1 = create_node(5, 2)
    poly1.next = create_node(4, 1)
    poly1.next.next = create_node(2, 0)

    # Create second list of 5x^1 + 5x^0
    poly2 = create_node(5, 1)
    poly2.next = create_node(5, 0)

    print("1st Number: ", end="")
    show(poly1)

    print("2nd Number: ", end="")
    show(poly2)

    print("Added polynomial: ", end="")

    # Function to add two polynomial numbers
    addPolynomial(poly1, poly2)

Time Complexity: O((m + n)log(m+n)) where m and n are numbers of nodes in first and second lists respectively and we are using a map for adding the coefficients extra log(m+n) factor is added.