Add Two Numbers

add_two_numbers.go

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 * Runtime: 8 ms, faster than 88.19% of Go online submissions for Add Two Numbers.
 * Memory Usage: 4.3 MB, less than 100.00% of Go online submissions for Add Two Numbers.
 */
var one = ListNode{ Val: 1 }

func addTwoNumbers(l1 *ListNode, l2 *ListNode) *ListNode {
    if l1 == nil && l2 == nil {
        return nil
    } else if l1 == nil {
        return l2
    } else if l2 == nil {
        return l1
    }
    
    var sum int
    var o *ListNode 
    
    sum = l1.Val + l2.Val
    
    if sum > 9 {
        o = &one
    }
    
    l1.Val = sum % 10
    l1.Next = addTwoNumbers(
        addTwoNumbers(l1.Next, l2.Next),
        o,
    )
    
    return l1
}