1. 编写一段代码，将a设置为一个n个随机数的数组，要求随机数介于0（包含）和n（不包含）之间。
//import java.lang.Math
def getArray(n:Int)={
val nums = new Array[Int](n)
for(i <- 0 until nums.length){
nums(i) = (Math.random() * n).toInt
}
nums
}
getArray(10)
//res18: Array[Int] = Array(5, 1, 6, 9, 0, 9, 6, 6, 8, 1)
方法二：
object App{
def main(args: Array[String]){
makeArr(10).foreach(println)
}
def makeArr(n:Int): Array[Int]={
val a = new Array[Int](n)
val rand = new scala.util.Random()
for(i <- a) yield rand.nextInt(n)
}
}
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)经过置换后变为Array(2,1,4,3,5)。
object App{
def main(args: Array[String]){
val a = Array(1,2,3,4,5)
exchangeArr(a).foreach(println)
}
def exchangeArr(a:Array[Int]):Array[Int]={
for(i <- 0 until a.length){
if(i % 2 == 0 && i != a.length -1){
val t = a(i)
a(i) = a(i+1)
a(i+1) = t
}
}
a
}
}
3. 重复前一个练习，不过这一次生成一个新的值交换过的数组。用for/yield。
object App{
def main(args: Array[String]){
val a = Array(1,2,3,4,5)
val b = revertYield(a)
a.foreach(println)
println
b.foreach(println)
}
def revertYield(arr:Array[Int])={
for(i <- 0 until arr.length) yield {
if(i % 2 == 0 && i != arr.length -1){
arr(i+1)
}else if(i % 2 == 1 && i != arr.length -1){
arr(i-1)
}else if(i % 2 == 0 && i == arr.length -1){
arr(i)
}else{
arr(i-1)
}
}
}
}
4. 给定一个整数数组，产出一个新的数组，包含原数组中的所有正值，以原有顺序排列，之后的元素是所有零或负值，以原有顺序排列。
object App{
def main(args: Array[String]){
val a = Array(1,2,-3,-4,5,0)
sortArr(a).foreach(println)
}
def sortArr(arr:Array[Int])={
val positiveIndexes = for(i <- 0 until arr.length if arr(i) >0 ) yield i
val nonpositiveIndexes = for(i <- 0 until arr.length if arr(i) <= 0) yield i
val newArr = new Array[Int](arr.length)
for(i <- 0 until arr.length){
if(i < positiveIndexes.length) newArr(i) = arr(positiveIndexes(i))
else newArr(i) = arr(nonpositiveIndexes(i - positiveIndexes.length))
}
newArr
}
}
5. 如何计算Array[Double]的平均值？
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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？
object App{
def main(args: Array[String]){
val a = Array(1,2,-3,-4,5)
println(a.mkString("[",",","]"))
println(reverseArray(a).mkString("[",",","]"))
}
def reverseArray(arr:Array[Int])={
for(i <- 0 until arr.length/2){
val t = arr(arr.length-1-i)
arr(arr.length-1-i) = arr(i)
arr(i) = t
}
arr
}
}
/*result:
[1,2,-3,-4,5]
[5,-4,-3,2,1]
*/
ArrayBuffer的版本几乎和Array的版本一样。
import scala.collection.mutable.ArrayBuffer
object App{
def main(args: Array[String]){
val a = ArrayBuffer(1,2,-3,-4,5)
println(a.mkString("[",",","]"))
println(reverseArray(a).mkString("[",",","]"))
}
def reverseArray(arr:ArrayBuffer[Int])={
for(i <- 0 until arr.length/2){
val t = arr(arr.length-1-i)
arr(arr.length-1-i) = arr(i)
arr(i) = t
}
arr
}
}
/*result:
[1,2,-3,-4,5]
[5,-4,-3,2,1]
*/
7. 编写一段代码，产出数组中的所有值，去掉重复项。（提示：查看Scaladoc）
object App{
def main(args: Array[String]){
val a = Array(6,2,2,6,7,5,2)
println(a.mkString("[",",","]"))
val b = a.distinct
println(b.mkString("[",",","]"))
}
}
/*result:
[6,2,2,6,7,5,2]
[6,2,7,5]
*/
8. 重新编写3.4节结尾的示例。收集负值元素的下标，反序，去掉最后一个下标，然后对每一个下标调用a.remove(i)。比较这样做的效率和3.4节中另外两种方法的效率。
import scala.collection.mutable.ArrayBuffer
object App{
def main(args: Array[String]){
var a = ArrayBuffer(1,-2,3,-4,5,-6,7)
println(a.mkString("[",",","]"))
var begin = System.currentTimeMillis()
var b = ridAllNegativeButFirstA(a)
var end = System.currentTimeMillis()
println(end-begin)
println(b.mkString("[",",","]"))
println
a = ArrayBuffer(1,-2,3,-4,5,-6,7)
println(a.mkString("[",",","]"))
begin = System.currentTimeMillis()
b = ridAllNegativeButFirstB(a)
end = System.currentTimeMillis()
println(end-begin)
println(b.mkString("[",",","]"))
println
a = ArrayBuffer(1,-2,3,-4,5,-6,7)
println(a.mkString("[",",","]"))
begin = System.currentTimeMillis()
b = ridAllNegativeButFirstC(a)
end = System.currentTimeMillis()
println(end-begin)
println(b.mkString("[",",","]"))
}
def ridAllNegativeButFirstA(a:ArrayBuffer[Int])={
var first = true
var n = a.length
var i = 0
while(i < n){
if(a(i) >= 0) i += 1
else{
if(first) { first = false; i += 1 }
else { a.remove(i); n -= 1 }
}
}
a
}
def ridAllNegativeButFirstB(a:ArrayBuffer[Int])={
var first = true
val indexes = for(i <- 0 until a.length if first || a(i) >= 0) yield {
if (a(i) < 0) first = false; i
}
for(j <- 0 until indexes.length) a(j) = a(indexes(j))
a.trimEnd(a.length - indexes.length)
a
}
def ridAllNegativeButFirstC(a:ArrayBuffer[Int])={
val indexes = for(i <- 0 until a.length if a(i) < 0) yield i
val seq = indexes.reverse.dropRight(1)
for(i <- 0 until seq.length) a.remove(i)
a
}
}
/*result:
[1,-2,3,-4,5,-6,7]
5
[1,-2,3,5,7]
[1,-2,3,-4,5,-6,7]
4
[1,-2,3,5,7]
[1,-2,3,-4,5,-6,7]
3
[-2,-4,5,-6,7]
*/
9. 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。
import scala.collection.mutable.ArrayBuffer
import java.util.TimeZone
object App{
def main(args: Array[String]){
val a = TimeZone.getAvailableIDs()
val b = a.filter(_.startsWith("America/"))
for(i <- 0 until b.length) b(i) = b(i).replace("America/","")
b.foreach(println)
}
}
/*result:
Adak
Anchorage
Anguilla
Antigua
...
*/
10. 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。
（为什么用这样一个晦涩难懂的类？因为在Java标准类库中很难找得到使用java.util.List的代码。）
import scala.collection.JavaConversions.asScalaBuffer
import scala.collection.mutable.Buffer
import java.awt.datatransfer._
import java.util.TimeZone
object App{
def main(args: Array[String]){
val flavors = SystemFlavorMap.getDefaultFlavorMap().asInstanceOf[SystemFlavorMap]
val buffer = flavors.getNativesForFlavor(DataFlavor.imageFlavor)
println(buffer)
}
}
/*result
[PNG, JFIF, DIB, ENHMETAFILE, METAFILEPICT]
*/