2. Add Two Numbers

Medium

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.

解題

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func addTwoNumbers(l1 *ListNode, l2 *ListNode) *ListNode {
    p1 := l1
    p2 := l2
    ans := &ListNode{}
    now := ans
    carry := 0
    
    for p1 != nil || p2 != nil {
        sum := carry
        
        if p1 != nil {
            sum += p1.Val
            p1 = p1.Next
        }
        if p2 != nil {
            sum += p2.Val
            p2 = p2.Next
        }
        
        carry = sum / 10
        now.Next = &ListNode{Val: sum % 10}
        now = now.Next
    }
    
    if carry > 0 {
		now.Next = &ListNode{Val: carry}
	}
    
    return ans.Next
}