LeetCode-Add Two Numbers

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

Hide Tags Linked List Math

这道题在原理上很简单，模拟了加法的运算。但如何使code写的简洁是个难点，另外运用到了前置节点和遍历节点的技术。

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        if(l1==null && l2 == null){
            return null;
        }
        else if(l1 != null && l2 == null){
            return l1;
        }
        else if(l2 != null && l2 == null){
            return l2;
        }
        
        ListNode dummy = new ListNode(-1);
        ListNode end = dummy;
        int carry =0;
        while(l1 != null || l2 != null || carry !=0){
            int current =0;
            if(l1 != null){
                current = current + l1.val;
                l1 = l1.next;
            }
            if(l2 != null){
                current = current +l2.val;
                l2 = l2.next;
            }
            if(carry !=0 ){
                current = current + carry;
            }
            
            end.next = new ListNode(current%10);
            carry = current / 10;
            end = end.next;
        }
        return dummy.next;
        
    }
}

 二刷：

/**
 * 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) {
        
        int carry = 0;
        ListNode dummy = new ListNode(-1);
        ListNode cur = dummy;
        while(l1 != null || l2 != null){
            
            int sum = 0;
            if(l1 == null){
                sum = l2.val + carry;
                l2 = l2.next;
            }
            else if(l2 == null){
                sum = l1.val + carry;
                l1 = l1.next;
            }
            else{
                sum = l1.val + l2.val + carry;
                l1 = l1.next;
                l2 = l2.next;
            }
            if(sum >= 10){
                carry = 1;
                sum = sum -10;
            }
            else{
                carry = 0;
            }
            ListNode temp = new ListNode(sum);
            cur.next = temp;
            cur = temp;
        }
        if(carry == 1){
            ListNode temp = new ListNode(carry);
            cur.next = temp;
        }
        return dummy.next;

    }
}