CPMagical CP Library

Problem solution · C++

Add Two Polynomials Represented as Linked Lists

Add Two Polynomials Represented as Linked Lists: a C++ solution using direct simulation. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Direct simulation
Source
walkccc LeetCode Solutions
Length
56 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Direct simulation

For Add Two Polynomials Represented as Linked Lists, the implementation follows the problem’s operations directly while maintaining only the state needed for the next decision.

  1. Translate each rule into one explicit state update.
  2. Maintain the invariant after every processed item.
  3. Return the accumulated state once all relevant input has been handled.

Code notes

  • 56 lines of C++ from the credited upstream file 1634.cpp.
  • The implementation visibly relies on sequence storage.
  • 3 loop blocks detected.

Complexity

Count the number and nesting of passes over the input, then include the maintained containers in the memory estimate.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeAdd Two Polynomials Represented as Linked Lists · C++C++
Use this to learn the idea, then write your own version.
/** * Definition for polynomial singly-linked list. * struct PolyNode { *   int coefficient, power; *   PolyNode *next; *   PolyNode(): coefficient(0), power(0), next(nullptr) {}; *   PolyNode(int x, int y): coefficient(x), power(y), next(nullptr) {}; *   PolyNode(int x, int y, PolyNode* next): coefficient(x), power(y), *                                           next(next) {}; * }; */ class Solution { public:  PolyNode* addPoly(PolyNode* poly1, PolyNode* poly2) {    PolyNode* dummy = new PolyNode();    PolyNode* curr = dummy;    PolyNode* p = poly1;  // poly1's pointer    PolyNode* q = poly2;  // poly2's pointer     while (p != nullptr && q != nullptr) {      if (p->power > q->power) {        curr->next = new PolyNode(p->coefficient, p->power);        curr = curr->next;        p = p->next;      } else if (p->power < q->power) {        curr->next = new PolyNode(q->coefficient, q->power);        curr = curr->next;        q = q->next;      } else {  // p->power == q->power        const int sumCoefficient = p->coefficient + q->coefficient;        if (sumCoefficient != 0) {          curr->next = new PolyNode(sumCoefficient, p->power);          curr = curr->next;        }        p = p->next;        q = q->next;      }    }     while (p != nullptr) {      curr->next = new PolyNode(p->coefficient, p->power);      curr = curr->next;      p = p->next;    }     while (q != nullptr) {      curr->next = new PolyNode(q->coefficient, q->power);      curr = curr->next;      q = q->next;    }     return dummy->next;  }};

Keep practising

Did this explanation save you time? I'm a Grade 11 student building this free library to make difficult algorithms easier to understand.

Buy me a coffee ↗