[leetcode] Add Two Numbers

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From : https://leetcode.com/problems/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

/** * 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) return l2;        if(!l2) return l1;        int carry=0, sum;        ListNode* thead = new ListNode(0), *pre=thead;        while(l1 && l2) {            sum = l1->val + l2->val + carry;            carry = sum>9;            ListNode *node = new ListNode(sum%10);            pre->next = node;            pre = node;            l1 = l1->next;            l2 = l2->next;        }        while(l1) {            sum = l1->val + carry;            carry = sum>9;            ListNode *node = new ListNode(sum%10);            pre->next = node;            pre = node;            l1 = l1->next;        }        while(l2) {            sum = l2->val + carry;            carry = sum>9;            ListNode *node = new ListNode(sum%10);            pre->next = node;            pre = node;            l2 = l2->next;        }        if(carry) {            ListNode *node = new ListNode(1);            pre->next = node;        }        pre = thead->next;        delete thead;        return pre;    }};

/** * 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) return l2;        if(!l2) return l1;        int carry=0, sum, a, b;        ListNode* thead = new ListNode(0), *pre=thead;        while(l1 || l2) {            a=b=0;            if(l1) {a=l1->val; l1=l1->next; }            if(l2) {b=l2->val; l2=l2->next; }            sum = a + b + carry;            carry = sum>9;            ListNode *node = new ListNode(sum%10);            pre->next = node;            pre = node;        }        if(carry) pre->next = new ListNode(1);        pre = thead->next;        delete thead;        return pre;    }};

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