[LeetCode] 0021 Merge Two Sorted Lists

Merge Two Sorted Lists

LeetCode - 0021 Merge Two Sorted Lists
https://leetcode.com/problems/merge-two-sorted-lists/

Problem Description

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

Solution

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode dummyHead(0);  // to avoid potential memory leak
        auto currNode = &dummyHead;

        while(l1 && l2){
            auto &nextNode = (l1->val < l2->val) ? l1 : l2;
            currNode->next = nextNode;
            nextNode = nextNode->next;
            currNode = currNode->next;
        }

        currNode->next = l1 ? l1 : l2;
        return dummyHead.next;
    }
};

• Time complexity: O(n+m)
• Space complexity: O(1)