2.add-two-numbers.go

/*
 * @lc app=leetcode id=2 lang=golang
 *
 * [2] Add Two Numbers
 *
 * https://leetcode.com/problems/add-two-numbers/description/
 *
 * algorithms
 * Medium (30.36%)
 * Total Accepted:    740.6K
 * Total Submissions: 2.4M
 * Testcase Example:  '[2,4,3]\n[5,6,4]'
 *
 * 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
 * contain a single digit. Add the two numbers and return it as a linked list.
 * 
 * You may assume the two numbers do not contain any leading zero, except the
 * number 0 itself.
 * 
 * Example:
 * 
 * 
 * Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
 * Output: 7 -> 0 -> 8
 * Explanation: 342 + 465 = 807.
 * 
 * 
 */
/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func addTwoNumbers(l1 *ListNode, l2 *ListNode) *ListNode {
    carry := false
    result := &ListNode{}
    r := result

    for {
        if l1 == nil && l2 == nil && !carry {
            break
        }

        sum := 0

        if l1 != nil {
            sum += l1.Val
            l1 = l1.Next
        }

        if l2 != nil {
            sum += l2.Val
            l2 = l2.Next
        }
        
        if carry {
            sum++
        }

        if sum > 9 {
            carry = true
        } else {
            carry = false
        }
        
        r.Next = &ListNode{ Val: sum % 10 }
        r = r.Next
    }

    return result.Next 
}