内部哈希映射,其键类型为字符串,包含url,int类型的值包含访问次数.

C#中的示例：

// Outer hash map    
var visitsByDay = 
    new Dictionary<DateTime,VisitsByUrl>(currentDate,new VisitsByUrl());

...

// inner hash map
public class VisitsByUrl
{
    public Dictionary<string,int> Urls { get; set; }

    public VisitsByUrl()
    {
        Urls = new Dictionary<string,int>();
    }

    public void Add(string url)
    {
        if (Urls[url] != null)
            Urls[url] += 1;
        else
            Urls.Add(url,1);
    }
}