117 lines
3.3 KiB
Plaintext
117 lines
3.3 KiB
Plaintext
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---
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title: A scala exercise a day 1
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slug: a-scala-exercise-a-day-1
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date: 2016-11-16 10:44:41
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updated: 2020-09-04 12:44:34
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tags:
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- Scala
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category: 编程
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cover: /images/2020/09/2020090412164155.jpg
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summary: 编写一段代码，将 a 设置为一个 n 个随机整数的数组，要求随机数介于 [0, n) 之间。
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---
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1、编写一段代码，将 a 设置为一个 n 个随机整数的数组，要求随机数介于 `[0, n)` 之间。
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```scala
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def randomArray(n: Int) : Array[Int] = {
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(for (i <- 0 until n) yield (math.random * n).toInt).toArray
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}
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```
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2、编写一个循环，将整数数组中相邻的元素置换。例如，`Array(1, 2, 3, 4, 5)` 经过置换之后变为 `Array(2, 1, 4, 3, 5)`。
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```scala
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def transferArray(array: Array[Int]) : Array[Int] = {
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for (i <- array.indices if i % 2 == 1) {
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val temp = array(i)
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array(i) = array(i - 1)
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array(i - 1) = temp
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}
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array
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}
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```
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3、重复前一个练习，不过这次生成一个新的值交换过的数组。用 `for/yield`。
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```scala
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def transferArray(array: Array[Int]) : Array[Int] = {
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(for (i <- array.indices) yield {
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i % 2 match {
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case 1 => array(i - 1)
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case 0 => if (i + 1 == array.length) array(i) else array(i + 1)
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}
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}).toArray
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}
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```
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4、给定一个整数数组，产出一个新的数组，包含元素组中的所有正值，以原有顺序排列，之后的元素是所有的零或负值，以原有顺序排列。
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```scala
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def sortArray(array: Array[Int]) : Array[Int] = {
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val (left, right) = array.partition(_ > 0)
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left ++ right
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}
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```
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5、如何计算 `Array[Double]` 的平均值？
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```scala
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def arrayAverage(array: Array[Double]) : Double = {
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array.sum / array.length
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}
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```
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6、如何重新组织 `Array[Int]` 的元素将它们以反序排列？对于 `ArrayBuffer[Int]` 你又会怎么做呢？
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```scala
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def reverseAverage(array: Array[Int]) : Array[Int] = {
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for (i <- array.indices if i < array.length / 2) {
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val temp = array(i)
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array(i) = array(array.length - i - 1)
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array(array.length - i - 1) = temp
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}
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array
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}
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```
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对于 `ArrayBuffer` 如下
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```scala
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def reverseAverage(array: ArrayBuffer[Int]) : ArrayBuffer[Int] = {
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array.reverse
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}
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```
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7、编写一段代码，产出数组中的所有值，去掉重复项。
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```scala
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def distinctAverage(array: Array[Int]) : Array[Int] = {
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array.distinct
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}
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```
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8、创建一个由 `java.util.TimeZone.getAvailableIDs` 返回的时区集合，判断条件是它们在美洲。去掉 `"America/"` 前缀并排序。
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```scala
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val sortedAmericanZone = java.util.TimeZone.getAvailableIDs.filter(_.startsWith("America")).map(_.replaceFirst("America/", "")).sorted
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```
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9、引入 `java.awt.datatransfer._` 并构建一个类型为 `SystemFlavorMap` 类型的对象： `val flavors = SystemFlavorMap.getDefaultFlavorMap().asInstanceOf[SystemFlavorMap]` 然后以 `DataFlavor.imageFlavor` 为参数调用 `getNativesForFlavor` 方法，以 Scala 缓冲保存返回值。
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首先导入包
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```scala
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import java.awt.datatransfer._
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import scala.collection.JavaConversions._
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import scala.collection.mutable.Buffer
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```
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然后编码
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```scala
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val flavors = SystemFlavorMap.getDefaultFlavorMap().asInstanceOf[SystemFlavorMap]
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val flavor: Buffer[String] = flavors.getNativesForFlavor(DataFlavor.imageFlavor)
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```
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