2. Add Two Numbers

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 contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

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

读题

题目的意思是说，给定两个非空的链表，计算两个链表所表示数的和，返回一个结果的链表，其实可以看出来就是一个大数相加的思想

题解

public class Solution2 {
    public static ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode p1 = l1;
        ListNode p2 = l2;
        //表示进位数
        int jinwei = 0;
        ListNode result = new ListNode(0);
        
        //指向结果的node
        ListNode head = result;
        //当前计算节点的前一个节点引用
        ListNode pre = result;
        int a;
        int b;
        while(p1!=null||p2!=null||jinwei!=0){
            //如果节点的是空加数为0否则为节点的值
            a = (p1 == null?0:p1.val);
            b = (p2 == null?0:p2.val);
            //计算进位数和本位和
            result.val = (a + b +jinwei)%10;
            jinwei = (a + b +jinwei)/10;
            //将pre应用指向当前的计算节点
            pre = result;
            //创建一个新的节点result向后移动
            ListNode p = new ListNode(0);
            result.next = p;
            result = p;
            if(p1!=null)
                p1 = p1.next;
            if(p2!=null)
                p2 = p2.next;
        }
        //pre最终指向最后一个节点
        pre.next = null;
        return head;
    }

    public static void print(ListNode p) {
        while (p != null) {
            System.out.print(p.val);
            p = p.next;
            if (p != null) {
                System.out.print(" -> ");
            }
        }
    }

    public static void main(String[] args) {
        ListNode node1 = new ListNode(1);
        ListNode node2 = new ListNode(2);
        ListNode node3 = new ListNode(3);
        node1.next = node2;
        node2.next = node3;
        node3.next = null;
        
        ListNode node4 = new ListNode(2);
        ListNode node5 = new ListNode(1);
        ListNode node6 = new ListNode(7);
        node4.next = node5;
        node5.next = node6;
        node6.next = null;
        //Solution2.print(node1);
        Solution2.print(Solution2.addTwoNumbers(node1, node4));
    }
}