Sunday, February 15, 2015

LeetCode [2] Add Two Numbers

 2. Add Two Numbers

Medium

You are given two non-empty linked lists representing two non-negative integers. 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.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.
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//C++: 40ms
/**
 * 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 *p1 = l1, *p2 = l2;
        ListNode *H = new ListNode(0), *p = H;
        int carry = 0;
        while(p1 || p2 || carry){
            int sum = carry;
            if(p1){
                sum += p1->val;
                p1 = p1->next;
            }
            if(p2){
                sum += p2->val;
                p2 = p2->next;
            }            
            ListNode *n = new ListNode(sum%10);
            p->next = n;
            p = n;
            carry = sum/10;
        }
        return H->next;
    }
};

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode p1 = l1, p2 = l2;
        ListNode H = new ListNode(), p = H;
        int c = 0;
        while(p1!=null || p2!=null){
            if(p1!=null){
                c += p1.val;
                p1 = p1.next;
            }
            if(p2!=null){
                c += p2.val;
                p2 = p2.next;
            }
            ListNode n = new ListNode(c%10);
            p.next = n;
            p = n;
            c = c/10;
        }
        
        if(c!=0){
            ListNode n = new ListNode(c);
            p.next = n;
        }
        return H.next;
    }
}

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