project Euler 15 可改進，用楊輝三角

時間是 0ms。

/**
 * Created by Administrator on 2015/5/21.
 */
public class E15 {
    public static long compute(long bigNumber,long smallNumber)
    {
        long result=1;
        long cycleIndex=bigNumber-smallNumber;
        int devide=1;
        for(long i=0;i<cycleIndex;i++)
        {
            result*=bigNumber--;
            result/=devide++;
        }
        return result;
    }

    public static void main(String[] args) {
        long stareTime=System.currentTimeMillis();
        long result=compute(40,20);
        System.out.println(result);
        long endTime=System.currentTimeMillis();
        System.out.println(endTime-stareTime+" ms");
    }
}