Why I’m not getting the testcases passed for LeetCode question number 189 even I am getting the expected output in browser console in JavaScript?

Are you frustrated because your code is not passing the test cases on LeetCode despite producing the expected output in the browser console? You’re not alone! This article will guide you through the common pitfalls and provide solutions to help you overcome the hurdle and get your code accepted by LeetCode.

Understanding the Problem

Before we dive into the solutions, let’s first understand the problem. LeetCode question number 189 is a classic “Rotate Array” problem, where you’re asked to rotate an array to the right by k steps. Sounds simple, right? But, as we’ll see, there are subtleties that can catch you off guard.

The Problem Statement

Given an array, rotate the array to the right by k steps, where k is non-negative.

Example 1:
Input: [1, 2, 3, 4, 5, 6, 7] and k = 3
Output: [5, 6, 7, 1, 2, 3, 4]
Explanation:
rotate 1 steps to the right: [7, 1, 2, 3, 4, 5, 6]
rotate 2 steps to the right: [6, 7, 1, 2, 3, 4, 5]
rotate 3 steps to the right: [5, 6, 7, 1, 2, 3, 4]

Why Is My Code Not Passing the Test Cases?

There are several reasons why your code might not be passing the test cases, even if it produces the expected output in the browser console. Let’s explore some common culprits:

• Incorrect Output Format: Are you returning the rotated array in the correct format? Make sure you’re not returning a console log or an alert instead of the actual array.
• Unintended Mutations: Are you modifying the original array? LeetCode expects you to return a new rotated array without altering the original.
• : Have you considered edge cases like an empty array, an array with a single element, or k being greater than the array length?
• Type Coercion: Are you using the correct data types? Ensure that you’re not coercing numbers to strings or vice versa.
• Browser Console vs. LeetCode Environment: The browser console and LeetCode environment have different interpreter behaviors. What works in the console might not work in LeetCode.

Solutions and Workarounds

Now that we’ve identified the potential issues, let’s provide solutions and workarounds to help you pass the test cases:

Use a Temporary Array

Create a temporary array to store the rotated elements, and then return the new array. This ensures that you’re not modifying the original array.

function rotate(nums, k) {
  const temp = nums.slice();
  for (let i = 0; i < k; i++) {
    temp.unshift(temp.pop());
  }
  return temp;
}

Handle Edge Cases

Make sure to handle edge cases by checking for empty arrays, arrays with a single element, and k being greater than the array length.

function rotate(nums, k) {
  if (nums.length === 0) return [];
  if (nums.length === 1) return nums;
  k = k % nums.length; // handle k being greater than the array length
  const temp = nums.slice();
  for (let i = 0; i < k; i++) {
    temp.unshift(temp.pop());
  }
  return temp;
}

Avoid Type Coercion

Use the correct data types and avoid coercing numbers to strings or vice versa. Ensure that your function returns an array of numbers, not strings.

function rotate(nums, k) {
  const temp = nums.slice();
  for (let i = 0; i < k; i++) {
    temp.unshift(Number(temp.pop())); // ensure numbers are not coerced to strings
  }
  return temp;
}

node
> const rotate = (nums, k) => {
...   const temp = nums.slice();
...   for (let i = 0; i < k; i++) {
.....     temp.unshift(temp.pop());
.....   }
...   return temp;
... }
> rotate([1, 2, 3, 4, 5, 6, 7], 3)
[ 5, 6, 7, 1, 2, 3, 4 ]