2. Add Two Numbers

Problem:

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.

思路：

Solution (C++):

ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
    ListNode l(0);
    ListNode* l3 = &l, *p = &l;
    
    int sum = 0, carry = 0;
    
    while (l1 && l2 ) {
        sum = l1->val + l2->val + carry;
        carry = sum / 10;
        sum %= 10;
        p->next = new ListNode(sum);
        p = p->next;
        l1 = l1->next;
        l2 = l2->next;
    }
    if (l1) {
        while (l1) {
            sum = l1->val + carry;
            carry = sum / 10;
            sum %= 10;
            p->next = new ListNode(sum);
            p = p->next;
            l1 = l1->next;
        }
    }
    if (l2) {
        while (l2) {
            sum = l2->val + carry;
            carry = sum / 10;
            sum %= 10;
            p->next = new ListNode(sum);
            p = p->next;
                l2 = l2->next;
        }
    }
    if (!l1 && !l2 && carry) { p->next = new ListNode(carry); p = p->next; }
        
    return l3->next;
}

性能：

Runtime: 28 ms  Memory Usage: 9.4 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB