Daily LeetCode Challenge (Day 12)#21. Merge Two Sorted Lists

Photo by Joshua Sortino on Unsplash

Difficulty | Easy

Challenge

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.

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]

Thought Process & Pseudo Code

• Check linked lists Reference in another article with a different challenge

Daily Leet Code Challenge: Add Two Numbers in a list node

• Get all elements from the list and add them to a single array
• sort the array
• loop through the elements and add them to a linked list
• return the list

Solution in php

/**
 * Definition for a singly-linked list.
 * class ListNode {
 *     public $val = 0;
 *     public $next = null;
 *     function __construct($val = 0, $next = null) {
 *         $this->val = $val;
 *         $this->next = $next;
 *     }
 * }
 */
class Solution {

    /**
     * @param ListNode $list1
     * @param ListNode $list2
     * @return ListNode
     */
    function mergeTwoLists($list1, $list2) {
        // get elements and add them to an array
        $num1 = [];
        
        while($list1){
            array_push($num1,$list1->val );
            $list1 = $list1->next;
        }

         while($list2){
            array_push($num1,$list2->val );
            $list2 = $list2->next;
        }

        // sort the array
        sort($num1);
        $list = null;
        // add to a new listnode
        $i=0;
        for($i = count($num1)-1; $i>=0; $i--){
             $list = new ListNode($num1[$i], $list );
        }
        return $list;
    }
}

Solution Javascript

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} list1
 * @param {ListNode} list2
 * @return {ListNode}
 */
var mergeTwoLists = function(list1, list2) {
    let numbers= [];

    while(list1){
        numbers.push(list1.val);
        list1 = list1.next;
    }

    while(list2){
        numbers.push(list2.val);
        list2 = list2.next;
    }
   //custom sort function to sort smallest to largest
   let sortedNumbers =   numbers.sort(function(a,b) { return a - b; });

    let list = null;

   for(let i= sortedNumbers.length-1; i >=0; i--){
       list = new ListNode(sortedNumbers[i], list);
   }
   return list;

};

PS: The challenges get easier with time 😁