// AddTwoNumbers.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
#include <cstdio>

struct ListNode {
    int val;
    ListNode* next;
    ListNode() : val(0), next(nullptr) {}
    ListNode(int x) : val(x), next(nullptr) {}
    ListNode(int x, ListNode* next) : val(x), next(next) {}

    void print()
    {
        ListNode* head = this;
        while (head)
        {
            printf("(%d)->", head->val);
            head = head->next;
        }
        printf("\n");
    }
};

class Solution {
private:
    static inline void iterate(ListNode*& l1, ListNode*& l2)
    {
        l1 = l1->next;
        l2 = l2->next;
    }

    static inline void iterate(ListNode*& l)
    {
        l = l->next;
    }

public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode* left = l1, *right = l2;
        ListNode* toRet = new ListNode();
        ListNode* current = toRet, *prev = nullptr;
       
        int carryover = 0;

        short val = (left->val + right->val);
        current->val = val % 10;
        carryover = val >= 10 ? 1 : 0;
        current->next = nullptr;
        prev = current;
        iterate(current);

        iterate(left, right);

        while (true)
        {
            if (left && right)
            {
                short val = (carryover + left->val + right->val);
                carryover = val >= 10 ? 1 : 0;
                current = new ListNode(val % 10, nullptr);
                prev->next = current;
                prev = current;                
                iterate(current);

                iterate(left, right);
            }
            else if (left || right)
            {
                ListNode** toAdd = left ? &left : &right;
                while (*toAdd)
                {
                    short val = (carryover + (*toAdd)->val);
                    carryover = val >= 10 ? 1 : 0;
                    current = new ListNode(val % 10, nullptr);

                    prev->next = current;
                    prev = current;
                    iterate(current);

                    iterate(*toAdd);
                }
            }
            else
            {
                if (carryover)
                {
                    current = new ListNode(1, nullptr);

                    prev->next = current;
                    prev = current;
                    iterate(current);
                }
                break;
            }
        }

        return toRet;
    }
};

int main()
{
    ListNode num1(9, new ListNode(9, nullptr)); // 32
    ListNode num2(9, new ListNode(9, new ListNode(9, nullptr))); // 54

    num1.print();
    num2.print();

    Solution s;
    s.addTwoNumbers(&num1, &num2)->print();

    return 0;
}

// Run program: Ctrl + F5 or Debug > Start Without Debugging menu
// Debug program: F5 or Debug > Start Debugging menu

// Tips for Getting Started: 
//   1. Use the Solution Explorer window to add/manage files
//   2. Use the Team Explorer window to connect to source control
//   3. Use the Output window to see build output and other messages
//   4. Use the Error List window to view errors
//   5. Go to Project > Add New Item to create new code files, or Project > Add Existing Item to add existing code files to the project
//   6. In the future, to open this project again, go to File > Open > Project and select the .sln file