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Cover image for Road to Genius: superior #62
Ilya Nevolin
Ilya Nevolin

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Road to Genius: superior #62

Each day I solve several coding challenges and puzzles from Codr's ranked mode. The goal is to reach genius rank, along the way I explain how I solve them. You do not need any programming background to get started, and you will learn a ton of new and interesting things as you go.

function swap(arr, [i, j], [m, n]) {
  const temp = arr[i][j];
  arr[i][j] = arr[m][n];
  arr[m][n] = temp;

function rotate(M) {
  const n = M.length;
  for (let i = 0; i < n-1; i++) {
    for (let j = 0; j < n-i; j++) {
      swap(M, [i, j], [n-j-1, n-i-1]);
  for (let i = 0; i < n/2; i++) {
    for (let j = 0; j < n; j++) {
      swap(M, [i, j], [n-i-1, j]);

let M = [
let A = M[2][1]

// A = ? (number)
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We've encountered this code a couple times before, it's about rotating a matrix by 90 degrees clockwise. By now this should be a piece of cake!

Here's some pseudocode:

M = [
 6 5 9
 8 1 5
 3 4 1

rotate 90°

M = [
 3 8 6
 4 1 5
 1 5 9
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To find the answer we need to find A = M[2][1] in the rotated matrix, which is 5 (on 3rd row and 2nd column).

coding challenge answer

By solving these challenges you train yourself to be a better programmer. You'll learn newer and better ways of analyzing, debugging and improving code. As a result you'll be more productive and valuable in business. Get started and become a certified Codr today at

Oldest comments (1)

This post blew up on DEV in 2020:

js visualized

🚀⚙️ JavaScript Visualized: the JavaScript Engine

As JavaScript devs, we usually don't have to deal with compilers ourselves. However, it's definitely good to know the basics of the JavaScript engine and see how it handles our human-friendly JS code, and turns it into something machines understand! 🥳

Happy coding!