class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        int carry=0;
        ListNode* res,*headptr;
        res=new ListNode(0);
        headptr=res;
        while(l1!=NULL||l2!=NULL){
            int sum = (l1==NULL?0:l1->val)+(l2==NULL?0:l2->val)+carry;
            carry = sum/10;
            res->next=new ListNode(sum%10);
            res=res->next;
            l1=l1==NULL?NULL:l1->next;
            l2=l2==NULL?NULL:l2->next;
        }
        if(carry) res->next=new ListNode(1);
        return headptr->next;
    }
};

class Solution {
public:
    int addDigits(int num) {
        return num - ((num-1)/9)*9;
    }
};

#include <iostream>
#include <vector>
using namespace std;
class Solution {
    vector<int> myVec;
public:
    bool isHappy(int n) {
        if (std::find(myVec.begin(), myVec.end(), n) != myVec.end())
        {
            if(n!=1) return false;
        }
        myVec.push_back(n);
        int sum=0,m;
        m=n;
        while(m){
            sum+=(m%10)*(m%10);
            m/=10;
        }
        if(sum==1) return true;
        else return isHappy(sum);
    }
    
};