Problem List

Merge Two Sorted Lists

May 31, 2025 • Go • linked list, recursion • easy

Problem

You are given the heads of two sorted linked lists list1 and list2.
Merge the two lists into 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.

Approach

1. If either of the nodes are nil, return the other
2. Otherwise use the lower value node and skip to its next recursively

Performance

Runtime beats: 100%
Memory beats: 61%

Complexity

Time: O(n)
Space: O(n)

Go Solution

func mergeTwoLists(list1 *ListNode, list2 *ListNode) *ListNode {
    if list1 == nil {
        return list2
    }
    
    if list2 == nil {
        return list1
    }

    var node *ListNode
    if list1.Val < list2.Val {
        node = list1
        node.Next = mergeTwoLists(list1.Next, list2)
    } else {
        node = list2
        node.Next = mergeTwoLists(list1, list2.Next)
    }

    return node
}

LeetCode Problem Link