我在Coursera上问了这个问题,但没有人回复,所以我来到这里.
这是关于 Scala中功能编程原理课程的最后一个任务(Anagrams).
这是关于 Scala中功能编程原理课程的最后一个任务(Anagrams).
如果函数减法返回无序的次数,AnagramsSuite中的最后一次测试将失败.
此外,还需要函数wordOccurrences返回已排序的Occurrences.
那么,为什么发生的顺序很重要？
// sentenceAnagrams passes the Test
def subtract(x: Occurrences,y: Occurrences): Occurrences = ((y
foldLeft x.toMap)((result,current) => {
result.updated(current._1,result(current._1)-current._2)
}) filter (_._2>0)).toList.sortWith(_._1<_._1)
// Without sortWith,the sentenceAnagrams will fail to get the right answer
def subtract(x: Occurrences,result(current._1)-current._2)
}) filter (_._2>0)).toList
解决方法
因为它是
part of the definition：
/** `Occurrences` is a `List` of pairs of characters and positive integers saying * how often the character appears. * This list is sorted alphabetically w.r.t. to the character in each pair. * All characters in the occurrence list are lowercase. * * Any list of pairs of lowercase characters and their frequency which is not sorted * is **not** an occurrence list. * * Note: If the frequency of some character is zero,then that character should not be * in the list. */ type Occurrences = List[(Char,Int)]
List类型是有序的.如果相反他们使用Map(就像它本来的那样),那么这不会是一个问题.
