使用 Scala 的第一天和第一次尝试 - 放轻松！我正在尝试重写我拥有的一些旧 Java 代码，它只是一个函数，它接受两个数字并打印出从 x 到 y 的数字。例如，我有增量功能：
def increment(start: Int, finish: Int) = {
for (i <- start to finish) {
println("Current value (increasing from "+start+" to "+finish+") is "+i)
}
}
但是，我正在努力编写一个从头到尾递减的相应递减函数？我已阅读 Scala downwards or decreasing for loop? 但仍不确定
谢谢
【问题讨论】：
标签： scala
scala>def decrement(start: Int, finish: Int) = {
| for (i <- start to finish by -1)
| println("Current value (decreasing from "+start+" to "+finish+") is "+i);
| }
decrement: (start: Int,finish: Int)Unit
scala> decrement(10, 1)
Current value (decreasing from 10 to 1) is 10
Current value (decreasing from 10 to 1) is 9
Current value (decreasing from 10 to 1) is 8
Current value (decreasing from 10 to 1) is 7
Current value (decreasing from 10 to 1) is 6
Current value (decreasing from 10 to 1) is 5
Current value (decreasing from 10 to 1) is 4
Current value (decreasing from 10 to 1) is 3
Current value (decreasing from 10 to 1) is 2
Current value (decreasing from 10 to 1) is 1
【讨论】：
start to finish by -1 将返回一个Range，您可以对其进行迭代。
def dec(start: Int, finish: Int) = { start to finish by -1 }; dec(10, 1).foreach( i => println("decrementing " + i) );
for (i <- (6 to 3 by -1)) {println ("i: " + i)}
i: 6
i: 5
i: 4
i: 3
如果你忘记了by -1，你可以向上移动并使用一个函数来恢复结果：
for (i <- (3 to 6)) {println ("i: " + ((6+3) - i))}
要排除第二个边界，请使用until：
for (i <- (6 until 3 by -1)) {println ("i: " + i)}
i: 6
i: 5
i: 4
或者，您可以为您的目的定义一个迭代器。扩展一个迭代器很容易；只需实现 'hasNext:Boolean' 和 'Next:[T]'，其中 T 是要处理的类型 - 在我们的例子中是 Int 或者 Long 或 BigInt：
class FromToIterator (start: Int, stop: Int) extends Iterator [Int] {
var current = start
// 3 6 3 6 6 3 6 3
def hasNext : Boolean = ((start < stop && current <= stop) || (start > stop && current >= stop))
def next: Int = {
val res = current
if (start < stop) current += 1 else current -= 1
res
}
}
val it = new FromToIterator (3, 6)
val ti = new FromToIterator (6, 3)
for (i <-it) println (i)
for (i <-ti) println (i)
【讨论】：
by -X 存在
这样您就可以在 Scala 中使用递减 for 循环。
object Example extends App {
for(i <- 20 to 2 by -2){
println("Value of i = "+ i)
}
}
------------------
O/P
------------------
Value of i = 20
Value of i = 18
Value of i = 16
Value of i = 14
Value of i = 12
Value of i = 10
Value of i = 8
Value of i = 6
Value of i = 4
Value of i = 2
【讨论】：
highnum to lownum by -1（与其他负步或正步切换以改变步进）
def decrement(start: Int, finish: Int) = {
for (i <- start to finish by -1) {
println("Current value (decreasing from "+start+" to "+finish+") is "+i)
}
}
【讨论】：
这是一个受Scala downwards or decreasing for loop?启发的全局递增/递减解决方案：
def goThrough(start: Int, finish: Int) = {
val d = if(start<=finish) 1 else -1
for (i <- start to finish by d) {
println("Current value (increasing from "+start+" to "+finish+") is "+i)
}
}
【讨论】：
object Test extends App{
def decrement(start: Int, finish: Int,dec :Int) = {
for (i <- Range(start,finish,dec)) {
println("Current value (decreasing from "+start+" to "+finish+") is "+i)
}
}
decrement(5,0,-1)
}
这也是一种方法。但可能不是最好的
【讨论】：
def printInDecreasingOrder(start : Int, end : Int){
if(start > end ){
for(i <- start to end by -1){
println(s"Current value (decreasing from $start to $end) is $i")
}
}else{
println("first num is smaller than second")
}
}
方法调用：
printInDecreasingOrder(10, 2)
结果：
当前值（从 10 减少到 2）是 10
当前值（从 10 减少到 2）是 9
当前值（从 10 减少到 2）是 8
当前值（从 10 减少到 2）是 7
当前值（从 10 减少到 2）是 6
当前值（从 10 减少到 2）是 5
当前值（从 10 减少到 2）是 4
当前值（从 10 减少到 2）是 3
当前值（从 10 减少到 2）是 2
printInDecreasingOrder(1, 10)
结果：
第一个 num 小于第二个
【讨论】：
如果您这样做，请在此答案中添加一点
for(j <- finish to start){......}
sbt 甚至没有显示错误。所以如果你想要一个递减的 for 循环，你需要这样做
for(j <- finish to start by -1){.......}
【讨论】：