Leetcode Merge Two Sorted Lists problem solution

YASH PAL, 31 July 202418 January 2026

In this Leetcode Merge Two Sorted Lists problem solution we need to Merge two sorted linked lists and return them as a sorted list. The list should be made by splicing together the nodes of the first two lists.

Leetcode Merge Two Sorted Lists problem solution

Leetcode Merge Two Sorted Lists problem solution in Python.

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        prehead = ListNode(-1)

        curr = prehead
        while l1 and l2:
            if l1.val <= l2.val:
                curr.next = l1
                l1 = l1.next
            else:
                curr.next = l2
                l2 = l2.next            
            curr = curr.next

        if l1 is not None:
            curr.next = l1
        else:
            curr.next = l2

        return prehead.next

Merge Two Sorted Lists problem solution in Java.

class Solution {
    
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode tmp = new ListNode(0);
        ListNode start = tmp;
        
        while (l1 != null || l2 != null) {
            if (l1 == null) {
                tmp.next = new ListNode(l2.val);
                tmp = tmp.next;
                l2 = l2.next;
            } else if (l2 == null) {
                tmp.next = new ListNode(l1.val);
                tmp = tmp.next;
                l1 = l1.next;
            } else {
                if (l1.val < l2.val) {
                    tmp.next = new ListNode(l1.val);                    
                    tmp = tmp.next;
                    l1 = l1.next;
                } else {
                    tmp.next = new ListNode(l2.val);
                    tmp = tmp.next;
                    l2 = l2.next;
                }
            }
        }
        
        return start.next;
    }
}

Problem solution in C++.

struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2){
    struct ListNode* head = NULL;
    struct ListNode* p= NULL;
    
    if(!l1){
        return l2;
    }
    if(!l2){
        return l1;
    }
    
    if(l2->val > l1->val){
        head = p = l1;
        l1 = l1->next;
    }
    else{
        head = p = l2;
        l2 = l2->next;
    }
    
    while(l1 && l2){
       if(l1->val > l2->val){
           p->next = l2;
           p = l2;
           l2 = l2->next;
       } 
       else{
           p->next = l1;
           p = l1;
           l1 = l1->next;
       }
    }
    
    if(l1){
        p->next = l1;
    }
    
    if(l2){
        p->next = l2;
    }
    
    
    return head;
}

Problem solution in C.

struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2){
    if(l2==NULL)
        return l1;
    else if(l1==NULL)
        return l2;
    if(l1->val<=l2->val){
        l1->next=mergeTwoLists(l1->next,l2);
        return l1;
     }
    else {
        l2->next=mergeTwoLists(l1,l2->next);
        return l2;
    }
}

coding problems solutions Leetcode Problems Solutions Leetcode

Leave a Reply