Leetcode and Lintcode

Add Two Numbers

Problem:

You have two numbers represented by a linked list, where each node contains a single digit. The digits are stored in reverse order, such that the 1’s digit is at the head of the list. Write a function that adds the two numbers and returns the sum as a linked list.

Have you met this question in a real interview? Yes

Example
Given 7->1->6 + 5->9->2. That is, 617 + 295.

Return 2->1->9. That is 912.

Given 3->1->5 and 5->9->2, return 8->0->8.

Solution:

This is an easay problem. Use a carry varible to store the carray and go through the two list from right to left doing addtion.

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/*************************************************************************
	> File Name: AddTwoNumbers.java
	> Author: Yao Zhang 
	> Mail: psyyz10@163.com 
	> Created Time: Mon 16 Nov 12:07:30 2015
 ************************************************************************/

public class AddTwoNumbers{
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        if (l1 == null && l2 == null)
            return null;
        
        int carry = 0;
        ListNode head = new ListNode(0);
        ListNode current = head;
        
        while (l1 != null || l2 != null){
            int sum = carry;
            
            if (l1 != null){
                sum += l1.val;
                l1 = l1.next;
            }            
            if (l2 != null){
                sum += l2.val;
                l2 = l2.next;
            }
                
            carry = sum / 10;
            current.next = new ListNode(sum % 10);
            current = current.next;
        }

        if (carry != 0){
            current.next = new ListNode(carry);
        }
        
        return head.next;
    }
}