project Euler 15 可改进，用杨辉三角

时间是 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");}}