Create a spiral matrix

spiral-matrix.js

// --- Directions
// Write a function that accepts an integer N
// and returns a NxN spiral matrix.
// --- Examples
//   matrix(2)
//     [[1, 2],
//     [4, 3]]
//   matrix(3)
//     [[1, 2, 3],
//     [8, 9, 4],
//     [7, 6, 5]]
//  matrix(4)
//     [[1,   2,  3, 4],
//     [12, 13, 14, 5],
//     [11, 16, 15, 6],
//     [10,  9,  8, 7]]

function matrix(n) {
  const result = [];
  for (let i = 0; i < n; i++) {
    result.push([]);
  }
  let startRow = 0;
  let endRow = n - 1;
  let startCol = 0;
  let endCol = n - 1;
  let count = 1;
  
  while (startRow <= endRow && startCol <= endCol) { 
    // fill start row from left to right and increment the startRow by 1
    for(let i = startCol; i <= endCol; i++) {
      result[startRow][i] = count;
      count++;
    } 
    // increment the startRow
    startRow += 1;
    
    // fill the end column from top to bottom and decrement the endCol by 1
    for(let i = startRow; i <= endRow; i++) {
      result[i][endCol] = count;
      count++
    }
    // decrement the endCol
    endCol -= 1;

    // fill the endRow from right to left and decrement the endRow by 1
    for(let i = endCol; i >= startCol; i--) {
      result[endRow][i] = count;
      count++
    } 
    // decrement the end row 
    endRow -= 1

    // fill the startCol from bottom to top and increment the startCol by 1
    for(let i = endRow; i >= startRow; i--) {
      result[i][startCol] = count;
      count++;
    }
    startCol += 1;
    // break;
  }
  return result;
}

// matrix(5);
module.exports = matrix;