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Algorithm

2. Add Two Numbers

Description

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.

Solution

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        if(l1==null||l2==null) return null;
        int value1,value2=0;
        ListNode pre = new ListNode(0);
        ListNode result = pre;
        while(l1!=null&&l2!=null){
            value1 = (l1.val+l2.val+value2)%10;
            value2 = (l1.val+l2.val+value2)/10;
            pre.next = new ListNode(value1);
            pre = pre.next;
            l1=l1.next;
            l2=l2.next;
            if(l1==null&&l2==null){
                break;
            }
            if(l1==null&&l2!=null){
                l1 = new ListNode(0);
            }
            if(l2==null&&l1!=null){
                l2 = new ListNode(0);
            }
        }
        if(value2>0){
            pre.next = new ListNode(value2);
        }
        return result.next;
    }
}

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