https://www.geeksforgeeks.org/inplace-rotate-square-matrix-by-90-degrees/

rotate-by-90-degree.js

// https://www.geeksforgeeks.org/inplace-rotate-square-matrix-by-90-degrees/
// https://practice.geeksforgeeks.org/problems/rotate-by-90-degree/0
function rotateMatrixAntiClockwise(matrix) {
  let x;
  let y;
  let length = matrix.length;
  // Consider all squares.
  // If the matrix is 3x3, you need to rotate one square.
  // If it's 4x4, or 5x5, it's gonna be two.
  // If it's 6x6, or 7x7, it's gonna be three.
  // "x" represents number of squares
  for (x = 0; x < length / 2; x++) {
    // "y" represents which square you're manipurating.
    // The range is x < y < length - x - 1
    // With 4x4 matrix, it'll be:
    //   0 < y < 4 - 0 - 1 ... The first (outside) square
    //   1 < y < 4 - 1 - 1 ... The second (inside) square
    for (y = x; y < length - x - 1; y++) {
      // 4x4 x=0 tmp=[0][0]1
      // 4x4 x=1 tmp=[1][1]6
      let tmp = matrix[x][y];
      // 4x4 x=0 [0][0] = [0][3]4
      // 4x4 x=1 [1][1] = [1][2]7
      matrix[x][y] = matrix[y][length-1-x];
      // 4x4 x=0 [0][3] = [3][3]16
      // 4x4 x=1 [1][2] = [2][2]11
      matrix[y][length-1-x] = matrix[length-1-x][length-1-y];
      // 4x4 x=0 [3][3] = [3][0]13
      // 4x4 x=1 [2][2] = [2][1]10
      matrix[length-1-x][length-1-y] = matrix[length-1-y][x];
      // 4x4 x=0 [3][0] = tmp
      // 4x4 x=1 [2][1] = tmp
      matrix[length-1-y][x] = tmp;
    }
  }
  return matrix;
}
function rotateMatrixClockwise(matrix) {
  let x;
  let y;
  let length = matrix.length;
  for (x = 0; x < length / 2; x++) {
    for (y = x; y < length - x - 1; y++) {
      // 4x4 x=0 y=0 tmp = [0][0]1
      // 4x4 x=0 y=1 tmp = [0][1]2
      // 4x4 x=0 y=2 tmp = [0][2]3
      // 4x4 x=1 y=1 tmp = [1][1]6
      let tmp = matrix[x][y];
      // 4x4 x=0 y=0 [0][0] = [3][0]13
      // 4x4 x=0 y=1 [0][1] = [2][0]9
      // 4x4 x=0 y=2 [0][1] = [1][0]5
      // 4x4 x=1 [1][1] = [2][1]10
      matrix[x][y] = matrix[length - 1 - y][x];

      // 4x4 x=0 y=0 [3][0] = [3][3]16
      // 4x4 x=0 y=1 [2][0] = [3][2]15
      // 4x4 x=0 y=2 [1][0] = [3][1]14
      // 4x4 x=1 [2][1] = [2][2]11
      matrix[length - 1 - y][x] = matrix[length - 1 - x][length - 1 - y];

      // 4x4 x=0 y=0 [3][3] = [0][3]4
      // 4x4 x=0 y=1 [3][2] = [1][3]8
      // 4x4 x=0 y=2 [3][1] = [2][3]12
      // 4x4 x=1 [2][2] = [2][1]7
      matrix[length - 1 - x][length - 1 - y] = matrix[y][length - 1 - x];

      // 4x4 x=0 [0][3] = tmp
      // 4x4 x=0 [1][2] = tmp
      matrix[y][length - 1 - x] = tmp;
    }
  }
  return matrix;
}
function printMatrix(matrix) {
  let idxX;
  let idxY;
  let length = matrix.length;
  let printArr = [];
  for (idxY = 0; idxY < length; idxY++) {
    for (idxX = 0; idxX < length; idxX++) {
      printArr.push(matrix[idxY][idxX]);
    }
    console.log(printArr.join(' | '));
    printArr = [];
  }
  console.log(matrix.map((row) => '-').join(' - '));
}
const matrixEx1 = [[1,2,3],[4,5,6],[7,8,9]];
// printMatrix(matrixEx1);
// printMatrix(rotateMatrixAntiClockwise(matrixEx1));
let matrix4x4 = [[1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,16]];
printMatrix(matrix4x4);
rotateMatrixAntiClockwise(matrix4x4);
printMatrix(matrix4x4);
rotateMatrixClockwise(matrix4x4);
printMatrix(matrix4x4);
const matrix6x6 = [[1,2,3,4,5,6],[7,8,9,10,11,12],[13,14,15,16,17,18],
[19,20,21,22,23,24],[25,26,27,28,29,30],[31,32,33,34,35,36]];
printMatrix(matrix6x6);
printMatrix(rotateMatrixAntiClockwise(matrix6x6));
printMatrix(rotateMatrixClockwise(matrix6x6));