/**
 * 
 */
package com.sunny.www.interview;

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Scanner;

/**
 * 使用随机数计算pi值
 * @author sunny
 *
 */
public class EstimatingPi {    

    public static double estimatingPi(long samplesCount){
        long inCircleCount = 0;    //落在圆以内的点（直径为单位1）
        for(int i = 0; i < samplesCount; i++){
            double x = Math.random();    //x坐标
            double y = Math.random();    //y坐标
            if(x * x + y * y < 1){    //到原点距离的平方<1, 表示点落在圆内部
                inCircleCount++;
            }
        }
        return BigDecimal.valueOf(4).multiply(BigDecimal.valueOf(inCircleCount)).divide(BigDecimal.valueOf(samplesCount), 5, RoundingMode.HALF_UP).doubleValue();
    }

    public static void main(String[] args) {
//        while(true){
//            Scanner sc = new Scanner(System.in);    //从控制台接收参数
//            long samplesCount = sc.nextLong();    //样本个数
//            System.out.println(EstimatingPi.estimatingPi(samplesCount));
//        }
        
        for(int i = 2; i <= 10; i++){
            long samplesCount = (long) Math.pow(10.0, Double.valueOf(String.valueOf(i)));
            System.out.println("EstimatingPi(" + samplesCount + ")=" + EstimatingPi.estimatingPi(samplesCount));
        }
    }

}

EstimatingPi(100)=3.16
EstimatingPi(1000)=3.244
EstimatingPi(10000)=3.1364
EstimatingPi(100000)=3.14236
EstimatingPi(1000000)=3.1403
EstimatingPi(10000000)=3.14198
EstimatingPi(100000000)=3.14144
EstimatingPi(1000000000)=3.14177