[2] Add Two Numbers | Leetcode Medium

문제설명

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.

결과예시

제한사항

• 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.

파이썬 코드

class Solution:
    def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode], c = 0) :
        val = l1.val + l2.val + c
        c = val//10
        ret = ListNode(val % 10)
        
        if( l1.next or l2.next or c != 0):
            if l1.next == None:
                l1.next = ListNode(0)
            if l2.next == None:
                l2.next = ListNode(0)
            ret.next = self.addTwoNumbers(l1.next, l2.next,c)
            
        return ret    

다른사람 코드

class Solution:
    def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
        res = dummy = ListNode()
        carry = 0
        while l1 or l2:
            v1, v2 = 0, 0
            if l1: v1, l1 = l1.val, l1.next
            if l2: v2, l2 = l2.val, l2.next
            
            val = carry + v1 + v2
            res.next = ListNode(val%10)
            res, carry = res.next, val//10
            
        if carry:
            res.next = ListNode(carry)
            
        return dummy.next

Time: O(n)
Space: O(1)