Software Enginner πŸ‡―πŸ‡΅ and πŸ‡°πŸ‡·

Leetcode - Add Two Numbers

Problem Add Two Numbers
Difficulty Medium
Language Java
Time complexity $$O(max(n, m))$$
Space complexity $$O(max(n, m) + 1)$$

Problem,

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, 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:

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.

Example 2:

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

Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]

Solution,

Reverse Order 라길래 λ©μ²­ν•˜κ²Œ μ²˜μŒμ—λŠ” Stack 으둜 μ§°λ‹€ (..). λ¬΄μ²™μ΄λ‚˜ 개발자 μŠ€λŸ½κ²Œλ„ 0 번 인덱슀λ₯Ό κ³ λ €ν•œ κ²ƒμ΄μ—ˆλ‹€. 제발 이런 λ©μ²­ν•œ μ‹€μˆ˜λŠ” ν•˜μ§€ 말자.

μ—°κ²° 리슀트λ₯Ό λκΉŒμ§€ νƒμƒ‰ν•˜λ©° λ”ν•˜λ©΄ 끝.

import java.util.*;

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode p1 = l1;
        ListNode p2 = l2;
        ListNode result = new ListNode(-1);
        ListNode ret = result;
        int carry = 0;
        while (p1 != null || p2 != null) {
            int val = (p1 != null ? p1.val : 0) + (p2 != null ? p2.val : 0) + carry;
            result.next = new ListNode(val % 10);
            result = result.next;
            carry = val / 10;
            
            if (p1 != null) p1 = p1.next;
            if (p2 != null) p2 = p2.next;
        }
        
        if (carry != 0) result.next = new ListNode(1);
        
        return ret.next;
    }
}