LeetCode2 Add Two Numbers 两数相加

1. problem description

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.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

2. solution

when two lists are not equally long, pad the shorter one with zero values. In this way, you don’t have to handle the remaining sublist.

ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
    ListNode *head = NULL, *prev = NULL;
    int carry = 0;
    while (l1 || l2) {
        int v1 = l1? l1->val: 0;
        int v2 = l2? l2->val: 0;
        int tmp = v1 + v2 + carry;
        carry = tmp / 10;
        int val = tmp % 10;
        ListNode* cur = new ListNode(val);
        if (!head) head = cur;
        if (prev) prev->next = cur;
        prev = cur;
        l1 = l1? l1->next: NULL;
        l2 = l2? l2->next: NULL;
    }
    if (carry > 0) {
        ListNode* l = new ListNode(carry);
        prev->next = l;
    }
    return head;
}