leetcode——Add Two Numbers

原題目：

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

解析：此題其實就是將兩個鏈表相應位置相加，並將存在一個鏈表中，注意進位。複雜度爲O(n)。

</pre><pre name="code" class="cpp">class Solution {
public:
	ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
		ListNode* list = new ListNode(0);
		ListNode* p = list;
		int carry = 0;
		while(l1 || l2)
		{
			int v1=0, v2=0, val=0;
			if(l1)
			{
				v1 = l1->val;
				l1 = l1->next;
			}	
			if(l2)
			{
				v2 = l2->val;
				l2 = l2->next;
			}	
			val = v1 + v2 + carry;
			carry = val / 10;
			p->next = new ListNode(val % 10);
			p = p->next;
		}
		if(carry)	p->next = new ListNode(carry);
		return list->next;
	}
};