UICollectionViewEwxtension.swift

extension UICollectionView {
    
    func dynamicGrid(numbersOfSquares :Float) -> (rows: Float, columns: Float, cellSize: CGSize) {
        
        let ratio: Float = Float(self.frame.size.width / self.frame.size.height)
        
        let numberOfColumns = sqrt(numbersOfSquares * ratio)
        let numberOfRows = numbersOfSquares / numberOfColumns;
        
        // Find best option filling the whole height
        
        var nrows1 = ceil(numberOfRows)
        var ncols1 = ceil(numbersOfSquares / nrows1)
        while (nrows1 * ratio < ncols1) {
            nrows1 += 1
            ncols1 = ceil(numbersOfSquares / nrows1)
        }
        let cellSize1 = Float(self.frame.size.height) / nrows1
        
        // Find best option filling the whole width
        var ncols2 = ceil(numberOfColumns)
        var nrows2 = ceil(numbersOfSquares / ncols2)
        while (ncols2 < nrows2 * ratio) {
            ncols2 += 1
            nrows2 = ceil(numbersOfSquares / ncols2)
        }
        let cellSize2 = Float(self.frame.size.width) / ncols2
        
        // Find the best values
        var nrows: Float = 0
        var ncols: Float = 0
        var cellSize: Float = 0
        
        if (cellSize1 < cellSize2) {
            nrows = nrows2
            ncols = ncols2
            cellSize = cellSize2
        } else {
            nrows = nrows1
            ncols = ncols1
            cellSize = cellSize1
        }
        
        return (rows: nrows, columns: ncols, cellSize: CGSize(width: Double(cellSize), height: Double(cellSize)))
    }
}