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

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解题思路：

本题解题思路与Add Binary一模一样，都是按位加，用flag记是否有进位，有是1，没有是0，不同的地方就是LinkedList的操作和String有一些区别，这点要特别注意！！当然我看到一个答案用的变量比我少，感觉更漂亮，也贴上来。

Add Binary   

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 Java code

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode result = new ListNode(0);
        ListNode p = result;
        ListNode p1 = l1, p2 = l2;
       
        int flag = 0;
        while(p1 != null || p2 != null){
            int v1 = 0, v2 = 0;
            if(p1 != null){
                v1 = p1.val;
                p1 = p1.next;
            }
            if(p2 != null){
                v2 = p2.val;
                p2 = p2.next;
            }
            int sum = v1+v2+flag;
            if(sum >= 10){
                p.next = new ListNode(sum -10);
                flag = 1;
            }else {
                p.next = new ListNode(sum);
                flag = 0;
            }
            p = p.next;
        }
        if(flag == 1){
            p.next = new ListNode(1);
        }
        return result.next;
    }
}

或者

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        int carry = 0;
        ListNode result = new ListNode(0);
        ListNode p1 = l1, p2 = l2, p3 = result;
        while(p1 != null || p2 != null){
            if(p1 != null){
                carry += p1.val;
                p1 = p1.next;
            }
            if(p2 != null){
                carry += p2.val;
                p2 = p2.next;
            }
            p3.next = new ListNode(carry%10);
            p3 = p3.next;
            carry /= 10;
        }
        if(carry == 1){
            p3.next = new ListNode(1);
        }
        return result.next;
    }

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Reference:

1. http://www.programcreek.com/2012/12/add-two-numbers/