Master the JavaScript interview with expertly curated questions and solutions. Strategies developed by FAANG engineers help you prep faster, boost confidence, and refine your problem-solving skills.

Master the JavaScript interview by practicing 20 carefully curated interview questions and solutions. These problems will provide the tools you need to tackle any question you find in an interview. Allow ~1 hour per question.

Most questions have multiple solutions presented. All solutions are thoroughly explained and time and space complexity are discussed. A passing familiarity with these ideas is expected. You'll learn how to tackle different types of problems so you can proceed with confidence in your interviews.

These questions go beyond the common problems that we've all seen. FizzBuzz and bubble sort? We start past those.

We'll discuss how to refine algorithms. We'll go over clever, advanced ways of manipulating data that interviewers are looking for. You'll walk away more skilled and confident in your problem solving and interviewing abilities.

This course is taught in ES2015.

Master the JavaScript Interview

## Instructions

Write a function that takes a square matrix as input. A square matrix has the same number of rows and columns, e.g. 3 x 3, 4 x 4, 5 x 5. It should return the same matrix rotated 90 degrees clockwise. The rotation should happen in place, meaning you may not create any extra matrixes or arrays in your function.

**Input**: Array of arrays of numbers

**Output**: Array of arrays of numbers

## Example

An input of:

    [[1, 2, 3],
     [4, 5, 6],
     [7, 8, 9]]

yields an output of:

    [[7, 4, 1],
     [8, 5, 2],
     [9, 6, 3]]

## Hints

1. Start at the border and work your way in.
2. We'll need some placeholder variables.

---

function rotateClockwise(mat) {
    // Your code here
}

# The Strategy

We'll treat the input matrix as a series of nested layers. We'll start from the outermost layer and work our way towards the center. Here's what that means, in terms of a 5x5 matrix.

If the matrix looks like this:

    [[01, 02, 03, 04, 05],
     [06, 07, 08, 09, 10],
     [11, 12, 13, 14, 15],
     [16, 17, 18, 19, 20],
     [21, 22, 23, 24, 25]]

We'll focus on the outer layer first. We'll pretend the inside doesn't even exist:

    [[01, 02, 03, 04, 05],
     [06,             10],
     [11,             15],
     [16,             20],
     [21, 22, 23, 24, 25]]

We'll go through and rotate the corners first. This means 01 goes to the right, 05 comes down. 25 goes left, and 21 goes up.

Then we'll send 02 to the right and down one, 10 down and to the left one, etc, etc. We'll do this until we've rotated every number in the layer.

Once the layer's done, we move inwards:

    [[                  ],
     [    07, 08, 09    ],
     [    12,     14    ],
     [    17, 18, 19    ],
     [                  ]]

We do the same thing. 7 goes right, 9 goes down, etc.

After this layer is processed, we're finished. We don't need to touch the center.






Learn how to rotate a matrix in place. We'll go over the complex algorithm required in heavy detail.

Introduction

Strings & Arrays

Advanced Strings & Arrays

Algorithms & Data Structures

JavaScript Mastery

Conclusion

Rotate Matrix, Advanced

Rotate Square Matrix in Place

Instructions

Example

Hints

Solution