算法－第四版－练习1.2.18解答

累加器的方差。以下代码为Accumulator类添加了var()和stddev()方法，它们计算了addDataValue()的方法的参数的方远大和标准差，验证这段代码。

/**
 * Description : 
 * Author      : mn@furzoom.com
 * Date        : Sep 26, 2016 10:35:26 AM
 * Copyright (c) 2013-2016, http://furzoom.com All Rights Reserved.
 */
package com.furzoom.lab.algs;

/**
 * ClassName    : Accumulator <br>
 * Function     : TODO ADD FUNCTION. <br>
 * date         : Sep 26, 2016 10:35:26 AM <br>
 * 
 * @version 
 */
public class Accumulator
{
    private double m;
    private double s;
    private int n;
    
    public void addDataValue(double val)
    {
        n++;
        s = s + 1.0 * (n - 1) / n * (val - m) * (val - m);
        m = m + (val - m) / n;
    }
    
    public double mean()
    {
        return m;
    }
    
    public double var()
    {
        return s / (n - 1);
    }
    
    public double stddev()
    {
        return Math.sqrt(this.var());
    }
    
    public String toString()
    {
        return String.format("%.5f %.5f", mean(), stddev());
    }
}

测试数据：

/**
 * Description : 
 * Author      : mn@furzoom.com
 * Date        : Sep 27, 2016 3:46:18 PM
 * Copyright (c) 2013-2016, http://furzoom.com All Rights Reserved.
 */
package com.furzoom.lab.algs.ch102;

import com.furzoom.lab.algs.Accumulator;

/**
 * ClassName    : E10218 <br>
 * Function     : TODO ADD FUNCTION. <br>
 * date         : Sep 27, 2016 3:46:18 PM <br>
 * 
 * @version 
 */
public class E10218
{
    public static void main(String[] args)
    {
        Accumulator acc = new Accumulator();
        acc.addDataValue(7);
        acc.addDataValue(8);
        acc.addDataValue(9);
        acc.addDataValue(10);
        System.out.println(acc);
    }

}

算法－第四版－1.2 数据抽象－习题索引汇总

算法－第四版习题索引汇总