21. Merge Two Sorted Lists

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:

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]

 

Constraints:

• The number of nodes in both lists is in the range [0, 50].
• -100 <= Node.val <= 100
• Both list1 and list2 are sorted in non-decreasing order.

Solution:

Go

package main

// Definition for singly-linked list.
type ListNode struct {
	Val  int
	Next *ListNode
}

func mergeTwoLists(list1 *ListNode, list2 *ListNode) *ListNode {
	if list1 == nil {
		return list2
	} else if list2 == nil {
		return list1
	} else if list1.Val < list2.Val {
		list1.Next = mergeTwoLists(list1.Next, list2)
		return list1
	} else {
		list2.Next = mergeTwoLists(list1, list2.Next)
		return list2
	}
}

Python

from definitions.listnode import ListNode


class Solution:
    def mergeTwoLists(self, list1: ListNode, list2: ListNode) -> ListNode:
        if list1 is None:
            return list2
        elif list2 is None:
            return list1
        elif list1.val < list2.val:
            list1.next = self.mergeTwoLists(list1.next, list2)
            return list1
        else:
            list2.next = self.mergeTwoLists(list1, list2.next)
            return list2

...