[leetcode] Add Two Numbers-优快云博客

本文提供了一种解决LeetCode上经典题目“两数相加”的方法。该题目要求将两个非负整数以链表形式表示，并以逆序方式存储每个节点的单个数字，然后将这两个数相加并返回结果链表。文章详细介绍了如何通过遍历两个链表并进行逐位相加来实现这一目标。

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2019独角兽企业重金招聘Python工程师标准>>>

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

https://oj.leetcode.com/problems/add-two-numbers/

思路：模拟题，从头向后依次遍历两个链表相加。

注意：1. 用dummy head简便处理。2. 注意carry的处理，尤其最高位进位的情况。3. 注意引用null的判断。

public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        // printList(l1);
        // printList(l2);
        ListNode p = new ListNode(-1);
        ListNode head = p;
        int c = 0;
        while (l1 != null || l2 != null || c == 1) {
            int curInt = 0;
            if (l1 != null)
                curInt += l1.val;
            if (l2 != null)
                curInt += l2.val;
            curInt += c;
            if (curInt > 9) {
                c = 1;
                curInt -= 10;
            } else
                c = 0;
            p.next = new ListNode(curInt);

            p = p.next;
            if (l1 != null)
                l1 = l1.next;
            if (l2 != null)
                l2 = l2.next;
        }

        // printList(head.next);

        return head.next;
    }

    void printList(ListNode node) {
        while (node != null) {
            System.out.print(node.val);
            if (node.next != null)
                System.out.print("->");
            node = node.next;
        }
        System.out.println();

    }

    public static void main(String[] args) {
        ListNode l1 = new ListNode(2);
        l1.next = new ListNode(4);
        l1.next.next = new ListNode(5);

        ListNode l2 = new ListNode(5);
        l2.next = new ListNode(6);
        l2.next.next = new ListNode(4);

        new Solution().addTwoNumbers(l1, l2);

    }

}

class ListNode {
    int val;
    ListNode next;

    ListNode(int x) {
        val = x;
        next = null;
    }
}