[LeetCode] [Medium] Add Two Numbers (linked list)

1. Problems

Given two num list 

 

Add the two numbers and return the sum 

 

2. Sol

I use triple pointer for update double pointer.

 

Becuse double pointer have address of answer list and I don't want to change value of answer list.

 

 

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    void pushList(ListNode*** l0, int sum) {
        if(**l0 == nullptr)
            **l0 = new ListNode(sum);
        else
        {
            (**l0)->next = new ListNode(sum);
            *l0 = &((**l0)->next);
        }
    }
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode* ret = nullptr;
        ListNode** tmp = &ret;
        int carry = 0;
        while(l1||l2||carry)
        {
            int sum = carry;
            if(l1) sum += l1->val, l1 = l1->next;
            if(l2) sum += l2->val, l2 = l2->next;
            pushList(&tmp, sum%10);
            carry = sum/10;
        }
        return ret;
    }
};