Add Two Numbers II Problem


Description

LeetCode Problem 445.

You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example 1:

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Input: l1 = [7,2,4,3], l2 = [5,6,4]
Output: [7,8,0,7]

Example 2:

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Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [8,0,7]

Example 3:

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Input: l1 = [0], l2 = [0]
Output: [0]

Constraints:

  • The number of nodes in each linked list is in the range [1, 100].
  • 0 <= Node.val <= 9
  • It is guaranteed that the list represents a number that does not have leading zeros.


Sample C++ Code

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/**
 * 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* h1, ListNode* h2) {
        stack<int> s1, s2;
        while (h1) {
            s1.push(h1->val);
            h1 = h1->next;
        }
        while (h2) {
            s2.push(h2->val);
            h2 = h2->next;
        }
        int carry_on = 0;
        ListNode *curr = NULL, *prev = NULL;
        while (s1.size() || s2.size() || carry_on) {
            int sum = carry_on;
            if (s1.size()) {
                sum += s1.top();
                s1.pop();
            }
            if (s2.size()) {
                sum += s2.top();
                s2.pop();
            }
            carry_on = sum / 10;
            prev = new ListNode(sum % 10);
            prev->next = curr;
            curr = prev;
        }
        return curr;
    }
};




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