add_two_numbers_ii.cpp

// 两数相加 II
// https://leetcode.cn/problems/add-two-numbers-ii
// INLINE  ../../images/stack/add_two_numbers_ii.jpeg

#include <headers.hpp>

/**
 * Definition for singly-linked list.
 * 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) {}
 * };
 */
class Solution {
public:
  ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
    stack<int> s1, s2;
    while (l1) {
      s1.push(l1->val);
      l1 = l1->next;
    }
    while (l2) {
      s2.push(l2->val);
      l2 = l2->next;
    }
    int carry = 0;
    ListNode *head = nullptr;
    while (!s1.empty() || !s2.empty() || carry != 0) {
      int sum = carry;
      if (!s1.empty()) {
        sum += s1.top();
        s1.pop();
      }
      if (!s2.empty()) {
        sum += s2.top();
        s2.pop();
      }
      ListNode *node = new ListNode(sum % 10);
      node->next = head;
      head = node;
      carry = sum / 10;
    }
    return head;
  }
};