Last updated on January 20th, 2025 at 10:52 pm

Here, we see a Merge Two Sorted Lists LeetCode Solution. This Leetcode problem is solved using different approaches in many programming languages, such as C++, Java, JavaScript, Python, etc.

List of all LeetCode Solution

Topics

Linked List

Companies

Amazon, Apple, LinkedIn, Microsoft

Level of Question

Easy

Merge Two Sorted Lists LeetCode Solution

1. Problem Statement

You are given the heads of two sorted linked lists list1 and list2. Merge the two lists in a one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list.

Example 1: (fig-1)
Input: list1 = [1,2,4], list2 = [1,3,4]
Output: [1,1,2,3,4,4]

Example 2:
Input: list1 = [], list2 = []
Output: []

Example 3:
Input: list1 = [], list2 = [0]
Output: [0]

2. Coding Pattern Used in Solution

The coding pattern used in the provided code is “K-way Merge”. This pattern is commonly used to merge multiple sorted lists or arrays into a single sorted list. In this case, the problem involves merging two sorted linked lists into one sorted linked list.

3. Code Implementation in Different Languages

3.1 Merge Two Sorted Lists C++

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
        if(list1 == NULL) return list2;
        if(list2 == NULL) return list1;
        if(list1->val>=list2->val) list2->next = mergeTwoLists(list1, list2-> next);
        else{
            list1->next = mergeTwoLists(list1->next, list2);
            list2 = list1;
        }return list2;
    }
};

3.2 Merge Two Sorted Lists Java

class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
		if(list1 == null) return list2;
		if(list2 == null) return list1;
		if(list1.val < list2.val){
			list1.next = mergeTwoLists(list1.next, list2);
			return list1;
		} else{
			list2.next = mergeTwoLists(list1, list2.next);
			return list2;        
    }
    }
}

3.3 Merge Two Sorted Lists JavaScript

var mergeTwoLists = function(list1, list2) {
    var mergedHead = { val : -1, next : null },
        crt = mergedHead;
    while(list1 && list2) {
        if(list1.val > list2.val) {
            crt.next = list2;
            list2 = list2.next;
        } else {
            crt.next = list1;
            list1 = list1.next;
        }
        crt = crt.next;
    }
    crt.next = list1 || list2;
    
    return mergedHead.next;    
};

3.4 Merge Two Sorted Lists Python

class Solution(object):
    def mergeTwoLists(self, list1, list2):
        dummy = cur = ListNode(0)
        while list1 and list2:
            if list1.val < list2.val:
                cur.next = list1
                list1 = list1.next
            else:
                cur.next = list2
                list2 = list2.next
            cur = cur.next
        cur.next = list1 or list2
        return dummy.next

4. Time and Space Complexity

	Time Complexity	Space Complexity
C++	O(n + m)	O(n + m)
Java	O(n + m)	O(n + m)
JavaScript	O(n + m)	O(1)
Python	O(n + m)	O(1)