Project Euler 113

/**
 * Copyright uwi ( http://wonderfl.net/user/uwi )
 * MIT License ( http://www.opensource.org/licenses/mit-license.php )
 * Downloaded from: http://wonderfl.net/c/z8Lz
 */

package {
    import flash.display.Sprite;
    import flash.text.TextField;
    import flash.utils.getTimer;
    // @see http://projecteuler.net/index.php?section=problems&id=113
    public class Euler113 extends Sprite {
        private var _tf : TextField;
  
        public function Euler113() {
            _tf = new TextField();
            _tf.width = 465;
            _tf.height = 465;
            addChild(_tf);
            
            var s : int = getTimer();
            _tf.appendText(solve().toString() + "\n");
            var g : int = getTimer();
            _tf.appendText((g - s).toString() + " ms\n");
        }
        
        private const N : int = 100;
        
        private function solve() : Number
        {
            var up : Number = c(N + 9, 9);
            var down : Number = 1;
            for(var i : int = 1;i <= N;i++)down += c(i + 9, 9) - 1;
            
            return up + down - (9 * N + 1) - 1;
        }
        
        private function c(n : int, k : int) : Number
        {
            var ret : Number = 1;
            if(k > n / 2)k = n - k;
            for(var a : int = n, b : int = 1;b <= k;a--,b++){
                ret *= a; ret /= b;
            }
            return ret;
        }
    }
}