在日期列表中找到最接近目标的日期的最佳方式？ [英] Best way to find date nearest to target in a list of dates?

问题描述

我有一个Date对象列表和一个目标日期。我想在列表中找到距离目标日期最近的日期，但仅在目标日期之前找到日期。

示例：
2008-10 -1
2008-10-2
2008-10-4

目标日期为2008-10-3，我想要2008-10-2

最好的方法是什么？

解决方案

Sietse de Kaper解决方案假定一个反向排序列表，绝对不是最自然的事情。

自然排序顺序java正在跟随自然排序顺序。 （请参阅Collection.sort http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collections.html#sort（java.util.List）文档）

从您的示例中，

 
目标日期= 2008-10-03 
列表= 2008-10-01 2008-10-02 2008-10-04 
 

如果另一个开发者使用您的方法与天真的方法，他会得到2008-10-01这不是预期的

不要对列表的排序做出假设。

如果你出于表现原因试图遵循最自然的惯例（按升序排列）

如果你真的要遵循另一个惯例，那么你真的应该记录下来。

 私人日期getDateNearest（列表&日期>日期，日期目标日期）{
日期returnDate = targetDate 
 for（日期日期：日期）{
 //如果当前迭代的日期是之前目标日期
 if（date.compareTo（targetDate）<= 0）{
 / /如果当前的迭代日期是after当前的返回日期
 if（date.compareTo（returnDate）> 0）{
 returnDate = date; 
} 
} 
} 
 return returnDate; 
} 
  

编辑 - 我也喜欢Treeset答案，但我认为可能会稍慢一些因为它等同于排序数据然后查找它们=> nlog（n）进行排序，然后文档意味着它是用于访问的log（n），因此将是nlog（n）+ log（n）vs n

I have a list of Date objects, and a target Date. I want to find the date in the list that's nearest to the target date, but only dates that are before the target date.

Example: 2008-10-1 2008-10-2 2008-10-4

With a target date of 2008-10-3, I want to get 2008-10-2

What is the best way to do it?

解决方案

Sietse de Kaper solution assumes a reverse sorted list, definitely not the most natural thing to have around

The natural sort order in java is following the ascending natural ordering. (see Collection.sort http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collections.html#sort(java.util.List) documentation)

From your example,

target date = 2008-10-03 
list = 2008-10-01 2008-10-02 2008-10-04 

If another developper uses your method with a naive approach he would get 2008-10-01 which is not what was expected

Don't make assumptions as to the ordering of the list.

If you have to for performance reasons try to follow the most natural convention (sorted ascending)

If you really have to follow another convention you really should document the hell out of it.

private Date getDateNearest(List<Date> dates, Date targetDate){
  Date returnDate = targetDate
  for (Date date : dates) {
    // if the current iteration'sdate is "before" the target date
    if (date.compareTo(targetDate) <= 0) {
      // if the current iteration's date is "after" the current return date
      if (date.compareTo(returnDate) > 0){
        returnDate=date;
      }
    }
  }  
  return returnDate;
}

edit - I also like the Treeset answer but I think it might be slightly slower as it is equivalent to sorting the data then looking it up => nlog(n) for sorting and then the documentation implies it is log(n) for access so that would be nlog(n)+log(n) vs n

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