Leetcode学习笔记：#2 Add Two Numbers

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于 2019-05-05 16:24:44 发布

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该博客是Leetcode #2 Add Two Numbers的学习笔记。题目给出两个非空链表代表非负整数，数字逆序存储，要求将两数相加并以链表返回。解题需注意链表是逆序的，实现时要保存一个carry位，用于下一个节点相加。

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Leetcode学习笔记：#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.

实现：

public ListNode addTwoNumbers(ListNode l1, ListNode l2){
	ListNode dummyHead = new ListNode(0);
    ListNode p = l1, q = l2, curr = dummyHead;
    int carry = 0;
    while (p != null || q != null) {
        int x = (p != null) ? p.val : 0;
        int y = (q != null) ? q.val : 0;
        int sum = carry + x + y;
        carry = sum / 10;
        curr.next = new ListNode(sum % 10);
        curr = curr.next;
        if (p != null) p = p.next;
        if (q != null) q = q.next;
    }
    if (carry > 0) {
        curr.next = new ListNode(carry);
    }
    return dummyHead.next;
}

思路：
注意题目链表是反的，并不是正常顺序的两个数字相加。
保存一个carry位，在下一个node相加的时候提取出来加入。