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2. Add Two Numbers

Posted on Edited on In Disqus:
Symbols count in article: 1.8k Reading time ≈ 2 mins.

O(max(m, n)) time

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# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        tail = dummy = ListNode(-1)
        c = 0
        while l1 or l2 or c:
            a = l1.val if l1 else 0
            b = l2.val if l2 else 0
            l1 = l1.next if l1 else l1
            l2 = l2.next if l2 else l2
            c, s = divmod(a + b + c, 10)
            tail.next = ListNode(s)
            tail = tail.next
        return dummy.next
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# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        tail = dummy = ListNode(-1)
        c = 0
        while l1 or l2 or c != 0:
            a = l1.val if l1 else 0
            b = l2.val if l2 else 0
            l1 = l1.next if l1 else l1
            l2 = l2.next if l2 else l2
            s = a + b + c
            tail.next = ListNode(s % 10)
            tail = tail.next
            c = s // 10
        return dummy.next
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/**
 * 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) {
        int c = 0;
        ListNode dummy_head(0), *tail = &dummy_head;
        while (l1 || l2 || c > 0) {
            int a = l1 ? l1->val : 0;
            int b = l2 ? l2->val : 0;
            l1 = l1 ? l1->next : l1;
            l2 = l2 ? l2->next : l2;
            int s = a + b + c;
            tail->next = new ListNode(s % 10);
            tail = tail->next;
            c = s / 10;
        }
        return dummy_head.next;
    }
};
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/**
 * 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) {
        int a = 0, b = 0, c = 0;
        ListNode *n1 = l1, *n2 = l2, dummy_head(-1), *t = &dummy_head;
        while (n1 || n2 || c > 0) {
            a = n1 ? n1->val : 0;
            b = n2 ? n2->val : 0;
            int s = a + b + c;
            t->next = new ListNode(s % 10);
            t = t->next;
            c = s / 10;
            n1 = n1 ? n1->next : n1;
            n2 = n2 ? n2->next : n2;
        }
        return dummy_head.next;
    }
};