多段階選抜 (Kotlin)


|多段階選抜|解答日|シリーズ:yieldの練習/ジェネレータを入れ子に/整数平方根・立方根の実装|
|:--|:--|:--|
|問題|　|http://nabetani.sakura.ne.jp/hena/ord24eliseq/<br>https://qiita.com/Nabetani/items/1c83005a854d2c6cbb69|
|Ruby|2014/8/2(当日)|https://qiita.com/cielavenir/items/9f15e29b73ecf98968a5|
|C#/Python|2014/8/4|https://qiita.com/cielavenir/items/a1156e6a4f71ddbe5dcb|
| |　|ここから上はdrop_prev_square/drop_prev_cubicをまとめる前の答案|
|Go/C#/Ruby/Python|2014/8/5|https://qiita.com/cielavenir/items/2a685d3080862f2c2c47|
|PHP/JavaScript|2014/9/9|https://qiita.com/cielavenir/items/28d613ac3823afbf8407|
|VB|2014/9/10|https://qiita.com/cielavenir/items/cb7266abd30eadd71c04|
|D|2015/12/21|https://qiita.com/cielavenir/items/47c9e50ee60bef2847ec|
|Perl|2017/3/10|https://qiita.com/cielavenir/items/6dfbff749d833c0fd423|
|Lua|2017/3/13|https://qiita.com/cielavenir/items/c60fe7e8da73487ba062|
|C++20(TS)|2017/3/15|https://qiita.com/cielavenir/items/e1129ca185008f49cbab (MSVC)<br>https://qiita.com/cielavenir/items/1cfa90d73d11bb7dc3d4 (clang)|
|F#|2017/3/17|https://qiita.com/cielavenir/items/a698d6a26824ff53de81|
|Boo/Nemerle|2017/5/13|https://qiita.com/cielavenir/items/e2a783f0fe4b0fe0ed48|
|Perl6|2017/5/15|https://qiita.com/cielavenir/items/656ea17fa96c865c4498|
|Kotlin|2017/5/25|https://qiita.com/cielavenir/items/9c46ce8d9d12e51de285|
|Crystal|2018/5/8|https://qiita.com/cielavenir/items/1815bfa6a860fd1f90db|
|MoonScript|2018/6/16|https://qiita.com/cielavenir/items/8b03cce0386f4537b5ad|
|Julia/Rust|2018/12/20|https://qiita.com/cielavenir/items/3ddf72b06d625da0c4a5|
|Nim|2018/12/26|https://qiita.com/cielavenir/items/5728944867e609fd52a7|
|Tcl|2018/12/31|https://qiita.com/cielavenir/items/76cbd9c2022b48c9a2c9|
|Pascal/Cobra|2019/1/16|https://qiita.com/cielavenir/items/81b81baf8dfc1f877903|
|Icon|2019/1/17|https://qiita.com/cielavenir/items/889622dcc721f5a4da24|
|Swift|2020/5/31|https://qiita.com/cielavenir/items/3b0b84a218e35d538f7f|
|Java/Groovy/Scala|2020/5/31|https://qiita.com/cielavenir/items/7f058203a8fd03b65870|
|V|2020/10/17|https://qiita.com/cielavenir/items/df30a6c101a97a713df5|
|Zig/Zen|2020/10/17|https://qiita.com/cielavenir/items/9cced9e4a94dcd70df0f|
|Pike|2020/11/2|https://qiita.com/cielavenir/items/3a8248f41611302b34fd|
|Vala/Smalltalk|2020/11/29|https://qiita.com/cielavenir/items/085dabe593cd916af5e8|
|Objective-C|2020/11/30|https://qiita.com/cielavenir/items/a1736e38789a3dd5cc5a|
|Ruby(Ractor)|2021/1/2|https://qiita.com/cielavenir/items/f493c6d512b63cc571cc|
|Python(_xxsubinterpreters)|2021/6/29|https://qiita.com/cielavenir/items/f1f581a055db918954f1|
|Falcon/Scheme|2021/9/5|https://qiita.com/cielavenir/items/c13d12cf44f0d17f4a94|
|Clojure/Lisp|2021/9/7|https://qiita.com/cielavenir/items/7458ba076f4e5bc0f196|
|(icbrtの実装に関する)補題|2017/5/11|整数除算であってもn/(x*y)はn/x/yに等しい(ことの証明)<br>https://qiita.com/cielavenir/items/21a6711afd6be8c18c55|

(最近あれな答案が続いていたので)まあまあきれいに書けたほうか。

```kotlin:hena24_enum.kt
//usr/bin/env kscript $0 $@;exit

// http://qiita.com/Nabetani/items/1c83005a854d2c6cbb69
// http://nabetani.sakura.ne.jp/hena/ord24eliseq/

import kotlin.sequences.*
fun isqrt(n:Int):Int{
	if(n<=0)return 0
	if(n<4)return 1
	var x=0
	var y=n
	while(x!=y&&x+1!=y){x=y;y=(n/y+y)/2}
	return x
}
fun icbrt(n:Int):Int{
	if(n<0)return -icbrt(-n)
	if(n==0)return 0
	if(n<8)return 1
	var x=0
	var y=n
	while(x!=y&&x+1!=y){x=y;y=(n/y/y+y*2)/3}
	return x
}
fun is_sq(n:Int):Boolean{
	val x=isqrt(n)
	return x*x==n
}
fun is_cb(n:Int):Boolean{
	val x=icbrt(n)
	return x*x*x==n
}
fun is_multiple(i:Int,n:Int):Boolean{return i%n==0}
fun is_le(i:Int,n:Int):Boolean{return i<=n}

fun generate():Sequence<Int>{
	return sequence{
		var i=1
		while(true){
			yield(i)
			i+=1
		}
	}
}
fun drop_prev(check:(Int)->Boolean,_prev:Sequence<Int>):Sequence<Int>{
	return sequence{
		val prev=_prev.iterator()
		var a=prev.next()
		var b=prev.next()
		while(true){
			if(!check(b))yield(a)
			a=b
			b=prev.next()
		}
	}
}
fun drop_next(check:(Int)->Boolean,_prev:Sequence<Int>):Sequence<Int>{
	return sequence{
		val prev=_prev.iterator()
		var a=prev.next()
		var b=prev.next()
		yield(a)
		while(true){
			if(!check(a))yield(b)
			a=b
			b=prev.next()
		}
	}
}
fun drop_n(check:(Int,Int)->Boolean,n:Int,_prev:Sequence<Int>):Sequence<Int>{
	return sequence{
		val prev=_prev.iterator()
		var i=0
		while(true){
			i+=1
			val a=prev.next()
			if(!check(i,n))yield(a)
		}
	}
}
fun main(args:Array<String>){
	val f: HashMap<Char,(Sequence<Int>)->Sequence<Int>> = hashMapOf(
		'S' to {e->drop_next(::is_sq,e)},
		's' to {e->drop_prev(::is_sq,e)},
		'C' to {e->drop_next(::is_cb,e)},
		'c' to {e->drop_prev(::is_cb,e)},
		'h' to {e->drop_n(::is_le,100,e)}
	)
	for(i in 2..9){
		f[('0'+i).toChar()] = fun(e)=drop_n(::is_multiple,i,e)
		//{e->drop_n(::is_multiple,i,e)} //both are OK
	}
	var line=readLine()
	while(line!=null){
		var first=true;
		//cS => f['S']!!(f['c']!!(generate()))
		for(n in line.toCharArray().fold(generate()){
			s,e->f[e]!!(s) //nullable? yippee
		}.take(10)){
			if(!first)print(',')
			first=false
			print(n)
		}
		println()
		System.out.flush()
		line=readLine()
	}
}
```

## 181024追記

コルーチン周りをKotlin 1.3(以降)のAPIにしました。Kotlin Nativeでコンパイルできることを確認しました。