g0001_0100.s0002_add_two_numbers.Solution.cpp Maven / Gradle / Ivy

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// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Math #Linked_List #Recursion
// #Data_Structure_II_Day_10_Linked_List #Programming_Skills_II_Day_15
// #Big_O_Time_O(max(N,M))_Space_O(max(N,M)) #2024_05_12_Time_16_ms_(82.17%)_Space_76.1_MB_(52.68%)

/**
 * 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:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode* dummyHead = new ListNode(0);
        ListNode* p = l1;
        ListNode* q = l2;
        ListNode* curr = dummyHead;
        int carry = 0;
        while (p != nullptr || q != nullptr) {
            int x = (p != nullptr) ? p->val : 0;
            int y = (q != nullptr) ? q->val : 0;
            int sum = carry + x + y;
            carry = sum / 10;
            curr->next = new ListNode(sum % 10);
            curr = curr->next;
            if (p != nullptr) {
                p = p->next;
            }
            if (q != nullptr) {
                q = q->next;
            }
        }
        if (carry > 0) {
            curr->next = new ListNode(carry);
        }
        return dummyHead->next;
    }
};