Add Two Numbers

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

题目意思就是 求俩个整数相加，整数是倒着表示的

我开始是用 l1 来存答案

/**
 * 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){
			return l2;
		}
		if (l2 == NULL){
			return l1;
		}
		ListNode *ans = l1;
		int cur = 0;
		ListNode *p=l1;
		while (l1 && l2){
			int temp = l1->val + l2->val + cur;
			l1->val = temp % 10;
			cur = temp / 10;
			p = l1;
			 l2 = l2->next;
			 if (l1->next == NULL && l2!=NULL){
				 l1->next = new ListNode(0);
				 l1 = l1->next;
				 break;
				
			 }
			 l1 = l1->next;
		}
		if (l1 == NULL && l2 == NULL && cur){
			ListNode * ff = ans;
			while (ff->next != NULL){
				ff = ff->next;
			}
			ff->next = new ListNode(1);
		
		}

		else if (l2!=NULL){
		while (l2 != NULL){
			int temp = cur + l2->val;

			l1->val = temp % 10;
			cur = temp / 10;
			l2 = l2->next;
			p = l1;
		
			l1->next = new ListNode(0);
			l1 = l1->next;

		 }
    		 if (cur){
    		  l1->val = 1;
    	  }
		}
		else if (l1!=NULL)
	  while(l1 != NULL){
		
			int temp = cur  + l1->val;
			l1->val = temp % 10;
			cur = temp /= 10;
			p = l1;
		
			if (l1->next == NULL &&  cur){
				l1->next = new ListNode(cur);
				l1->next->val = cur;
				l1 = l1->next;
				break;

			}
			
				l1 = l1->next;

	  }
	//  cout << ans->val << " " << ans->next->val << endl;
	  //cout << "fuck" << p->val << endl;
      
	 if (p->next && p->next->val == 0){
		  p->next = NULL;
	  }
		return ans;
	}
};

最好新建个链表保存答案

/**
 * 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) {
	
	
	ListNode *l=new ListNode(0);
	ListNode *cur = l;
	if (l1 == NULL){
		return l2;
	}
	if (l2 == NULL){
		return l1;
	}
	int ans = 0;
	int flag = 1;
	while (l1 != NULL || l2 != NULL){
		
		int val1 = 0;
		if (l1 != NULL){
			val1 = l1->val;
			l1 = l1->next;
		}
		int val2 = 0;
		if (l2 != NULL){
			val2 = l2->val;
			l2 = l2->next;
		}
		

		cur->next= new ListNode((val1 + val2 + ans) % 10);
		ans = (val1 + val2 + ans) / 10;
		cur = cur->next;

	}
	if (ans != 0){
		cur->next = new ListNode(ans);
	}
	return l->next;
}
};