Leetcode 445. Add Two Numbers II (Medium) (cpp)

Leetcode 445. Add Two Numbers II (Medium) (cpp)

Tag: Linked List

Difficulty: Medium

/*

445. Add Two Numbers II (Medium)

You are given two linked lists representing two non-negative numbers. The most significant digit comes first 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.

Follow up:
What if you cannot modify the input lists? In other words, reversing the lists is not allowed.

Example:

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

*/
/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
	ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
		if (l1 == NULL || l2 == NULL) {
			return l1 == NULL ? l2 : l1;
		}
		extend(l1, l2);
		ListNode *temp = add(l1, l2);
		return temp->val == 0 ? l1 : temp;
	}
private:
	int getLength(ListNode* l) {
		int res = 0;
		while (l != NULL) {
			res++;
			l = l->next;
		}
		return res;
	}
	void extend(ListNode*& l1, ListNode*& l2) {
		int len1 = getLength(l1), len2 = getLength(l2);
		while (len1 > len2) {
			ListNode *n = new ListNode(0);
			n->next = l2;
			l2 = n;
			len1--;
		}
		while (len1 < len2) {
			ListNode *n = new ListNode(0);
			n->next = l1;
			l1 = n;
			len2--;
		}
	}
	ListNode* add(ListNode* l1, ListNode* l2) {
		if (l1 == NULL) {
			return new ListNode(0);
		}
		l1->val += l2->val + add(l1->next, l2->next)->val;
		ListNode *tmp = new ListNode(l1->val / 10);
		l1->val %= 10;
		tmp->next = l1;
		return tmp;
	}
};