rotateMatrix, Javascript

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//JavaScript-C24.2.0 (SpiderMonkey)

print(rotateMatrix([[1,2,3], [4,5,6],[7,8,9]]));

// given an NxN matrix make a method to rotate it 90deg

/*
  [ 1 2 3 ]    [ 7 4 1 ]
  [ 4 5 6 ] -> [ 8 5 2 ]
  [ 7 8 9 ]    [ 9 6 3 ]
*/
function rotateMatrix(matrix) {
  if (!matrix || matrix.length === 0 || matrix.length !== matrix[0].length) {
    throw new Error('invalid matrix');
  }
  if (matrix.length < 2) {
    return matrix; // no need to do anything to rotate a 1,1 matrix
  }

let len = matrix.length - 1;
  let half = Math.floor(matrix.length / 2);
  // loop through diagonal
  for (let start = 0; start < half; start++) {
    // loop through x axis
    for (let i = 0; i < len - (start * 2); i++) {
      let y = start;
      let x = start + i;
      let prev = matrix[y][x];

// loop through all 4 sides
      for (let j = 0; j < 4; ++j) {
        let nextY = x;
        let nextX = len - y;
        let next = matrix[nextY][nextX];
        
        matrix[nextY][nextX] = prev;
        prev = next;
        
        x = nextX;
        y = nextY;
      }
    }
  }

return matrix;
}

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Absolute running time: 0.2 sec, cpu time: 0.14 sec, memory peak: 6 Mb, absolute service time: 0,21 sec