[Swift] Add Two Numbers

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]

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.

풀러가기

문제 이해

코드

func addTwoNumbers(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {
  var l1 = l1
  var l2 = l2
  
  var carry = 0
  var prev = ListNode()
  let ret = prev
  while l1 != nil || l2 != nil || carry != 0 {
    var sum = 0
    if l1 != nil {
      sum += l1!.val
      l1 = l1!.next
    }
    
    if l2 != nil {
      sum += l2!.val
      l2 = l2!.next
    }
    sum += carry
    
    carry = sum / 10
    
    let cur = ListNode(sum % 10)
    prev.next = cur
    prev = cur
  }
  
  return ret.next
}

풀이

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