Add Two Numbers

https://oj.leetcode.com/problems/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

下面是一个不能处理超长数据的答案。

/**

 * 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) {

        ListNode node = l1;

        int l1Value = 0;

        int count = 0;

        while(node != null){

            l1Value = l1Value + node.val * ((Double)Math.pow(10, count)).intValue();

            count ++;

            node = node.next;

        }

        

        node = l2;

        int l2Value = 0;

        count = 0;

        while(node != null){

            l2Value = l2Value + node.val * ((Double)Math.pow(10, count)).intValue();

            count++;

            node = node.next;

        }

        

        int sumValue = l1Value + l2Value;

        

        //int digits = (Math.floor((Double)(Math.log(sumValue) / Math.log(10) + 1)).intValue()); 

        int digits = String.valueOf(sumValue).length();

        if(sumValue < 10){

            digits = 1;

        }

        ListNode[] listNodes = new ListNode[digits];

        

        listNodes[0] = new ListNode(sumValue % 10);

        sumValue = sumValue / 10;

        

        for(int i = 1; i < digits; i++){

            listNodes[i] = new ListNode(sumValue % 10);

            listNodes[i - 1].next = listNodes[i];

            sumValue = sumValue / 10;

        }

        return listNodes[0];

    }

}

 下面是一个AC的方法。技巧是，对于为null的node，全部置为0，再运算。

/**

 * 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) {

        ListNode node1 = l1;

        ListNode node2 = l2;

        ListNode node_current = new ListNode(0);

        ListNode node_next = node_current;

        ListNode node_return = node_current;

        

        while(node1 != null || node2 != null){

            if(node1 == null){

                node1 = new ListNode(0);

            }

            if(node2 == null){

                node2 = new ListNode(0);

            }

            int sum = node1.val + node2.val + node_current.val;

            node_current.val = (node1.val + node2.val + node_current.val) % 10;

            if(sum > 9 || node1.next != null || node2.next !=null){

                node_next = new ListNode(sum / 10);

                node_current.next = node_next;

            }

            node_current = node_next;

            if(node1 != null){

                node1 = node1.next;

            }

            if(node2 != null){

                node2 = node2.next;

            }

        }



        return node_return;

    }

}