Learn essential coding patterns to answer problems and prepare for tech companies' interviews.

Ace the JavaScript Coding Interview

This module teaches us the underlying patterns behind common coding interview questions. By learning these essential patterns, we'll be able to unpack and answer any problem the right way—just by assessing the problem statement. This approach was created by FAANG hiring managers to help us prepare for the typical rounds of interviews at major tech companies like Apple, Google, Meta, Microsoft, and Amazon.

By the end of this module, we'll have the skills we need to unlock even the most challenging questions, grok the coding interview, and level up our career with confidence.

Coding Interview Patterns

# Statement

Given an $n \times n$ matrix, rotate the matrix 90 degrees clockwise. The performed rotation should be in place, i.e., the given matrix is modified directly without allocating another matrix. 

>**Note:** The function should only return the modified input matrix.

**Constraints:**

- `matrix.length` $=$ `matrix[i].length`
- $1 \leq$ `matrix.length` $\leq 20$
- $-10^3 \leq$ `matrix[i][j]` $\leq 10^3$

# Solution

The idea is to make groups of four cells and rotate them by 90 degrees clockwise.

Here's how the algorithm works:

1. We run a loop where `row` ranges from `0` to `n / 2`.

   1. Within this loop, we run a nested loop where `col` ranges from `row` to `n - row - 1`. These loops traverse the groups of four cells in the matrix. In this nested loop, we perform three swaps:

      1. The value of the top-left cell is swapped with the value of the top-right cell.

      2. The value of the top-left cell is swapped with the value of the bottom-right cell.

      3. The value of the top-left cell is swapped with the value of the bottom-left cell.

   2. The current group of four cells has been rotated by $90$ degrees. We now move to the next iteration of the outer loop to rotate the next group.

2. We repeat the process above until the whole matrix has been rotated.


Let’s look at the following illustration to get a better understanding of the solution:
  



Let's solve the Rotate Image problem using the Matrices pattern.