在scala中，如何使用模式匹配来匹配指定长度的列表？ [英] In scala, how can I use pattern match to match a list with specified length?

问题描述

我的代码如下所示：

  1 :: 2 ::无匹配{
案例1 :: ts :: Nil => 以1开始不止一个元素
 case 1 :: Nil => 开始于1.只有一个元素

  

我试着用 1 :: ts :: Nil 以匹配以 1 开头并且长度大于1的列表。它适用于2元素列表，但是，该模式不适用于 3元素列表，例如：

  1 :: 2 :: 3 :: Nil match {
 case 1 :: ts :: Nil => 以1开始不止一个元素
 case 1 :: Nil => 从1开始。只有一个元素

  

这不起作用。有人对此有何看法？

  1 ::无匹配{
 case 1 :: ts :: rest => 以1开始不止一个元素
 case 1 :: Nil => 从1开始。只有一个元素

  

一个列表或零，你确保该元素有超过1个元素与ts匹配，然后休息

My codes looks like this:

1::2::Nil match {
  case 1::ts::Nil => "Starts with 1. More than one element"
  case 1::Nil => "Starts with 1. Only one element"
}

I tried to use 1::ts::Nil to match the List who starts with 1 and whose length is greater than 1. It workes well for 2-element list, however, this pattern doesn't work for 3-element list, for example:

1::2::3::Nil match {
  case 1::ts::Nil => "Starts with 1. More than one element"
  case 1::Nil => "Starts with 1. Only one element"
}

This won't work..Does anyone have ideas about this?

解决方案

You don't have to match on Nil. What you could do instead is match on the rest.

1::Nil match {
   case 1::ts::rest => "Starts with 1. More than one element"
   case 1::Nil => "Starts with 1. Only one element"
}

With this code rest is than either a List or Nil and you make sure that the element has more than 1 element with the match on ts and then rest

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