spiral.js

/**
 * Returns a string concatenation of the elements of a matrix (2d array) in "spiral" order.
 * @param {[[]]} matrix - the 2d array
 * @param {string} [separator] - optional separator to use between values in string, defaults to ", "
 * @returns {string}
 */
function spiralMatrix(matrix, separator) {
	if (matrix.length === 0 || matrix[0].length === 0) {
		return "";
	}

	var firstRow = 0;
	var firstColumn = 0;
	var lastRow = matrix.length - 1;
	var lastColumn = matrix[0].length - 1;

	return spiralMatrixRecursive(matrix, firstRow, lastRow, firstColumn, lastColumn).join(separator || ", ");
}

function spiralMatrixRecursive(matrix, topRow, bottomRow, leftColumn, rightColumn) {
	var result = [];

	if (topRow > bottomRow || leftColumn > rightColumn) {
		return result;
	}

	var currentRow;
	var currentColumn;

	// loop through top row
	for (currentColumn = leftColumn; currentColumn <= rightColumn; currentColumn++) {
		result.push(matrix[topRow][currentColumn]);
	}

	// loop through rest of right column
	for (currentRow = topRow + 1; currentRow <= bottomRow; currentRow++) {
		result.push(matrix[currentRow][rightColumn]);
	}

	if (topRow !== bottomRow) {
		// loop through rest of bottom row
		for (currentColumn = rightColumn - 1; currentColumn >= leftColumn; currentColumn--) {
			result.push(matrix[bottomRow][currentColumn]);
		}
	}

	if (leftColumn !== rightColumn) {
		// loop through rest of left column (stop before top row as already done)
		for (currentRow = bottomRow - 1; currentRow > topRow; currentRow--) {
			result.push(matrix[currentRow][leftColumn]);
		}
	}

	return result.concat(spiralMatrixRecursive(matrix, topRow + 1, bottomRow - 1, leftColumn + 1, rightColumn - 1));
}

/**
 * Generates a matrix (2d array) with the given number of rows and columns,
 * containing random numbers between 1 and 10.
 * @param rows - number of rows
 * @param columns - number of columns
 * @returns {Array} - the matrix
 */
function generateMatrix(rows, columns) {
	var matrix = [];
	for (var i = 0; i < rows; i++) {
		matrix.push([]);

		for (var j = 0; j < columns; j++) {
			matrix[i][j] = Math.floor((Math.random() * 10) + 1);
		}
	}

	return matrix;
}