Question

任何人都可以解释：如何在子列表中拆分列表：

列表：

scala> val ls = List("P ", "PP ", "PP ", "PP ", "P ", "PP ", "PP ", "P ")

或者

scala> val ls = List("P", "PP", "PP", "PP", "P", "PP", "PP", "P")

子列表：

List("P", "PP", "PP", "PP"), List("P", "PP", "PP"), List("P")

已编辑 ::我真正想要的是在每次出现特定字符串时拆分列表！

TIA。

Answer 1

使用Include Irvine32.inc n=1000 n_terminal=31 ; terminal compare value is min(sqrt(n), 0FFFFh) (last value to process) ; no point to sieve beyond sqrt(n), because first unset multiply is ; sqrt(n)*sqrt(n) = n => beyond array ; and no point to sieve 10000h, because 10000h*10000h is out of 32b .data prime BYTE n DUP(?) .code main PROC ; fill array with "1" (from number 2 to n) mov edi,OFFSET prime+2 mov ecx,n-2 mov eax,1 ; eax=1 will be used also later (also ah=0) rep stosb ; set "0" and "1" as non-prime too mov WORD PTR [prime],cx ; (cx == 0 after "rep stosb") ; set "0" to all other non-primes by sieving mov esi,eax ; esi=1, start the loop as if "1" was handled last sieve_loop: inc esi ; next number to test ; sqrt(n) is enough to process, beyond that n <= number*number => out of array cmp esi,n_terminal ja sieve_end ; out of table, end sieving cmp prime[esi],al ; compare with "1" jne sieve_loop ; not a prime, don't flip the rest of sieve ; esi is prime, flip the other multiplies of it, starting from esi*esi (!) mov edi,esi ; esi*esi as smaller multiples are already covered by imul edi,edi ; smaller prime numbers sieving the array before flip_loop: cmp edi,n ; check if the multiply points beyond table jae sieve_loop ; if yes, continue main loop with next "prime" mov prime[edi],ah ; set this number to "0" (not prime) add edi,esi ; edi = next multiply of esi prime jmp flip_loop sieve_end: ; print all primes starting from 2 mov esi,eax ; esi = 1, as if "1" was handled last print_loop: inc esi ; while (++number < n) cmp esi,n jae end_print_loop cmp BYTE PTR prime[esi],1 ; eax/al is modified from "WriteDec" jne print_loop ; not a prime number, loop ; esi is prime number, print it mov eax,esi call WriteDec ; these two calls must preserve esi call Crlf jmp print_loop end_print_loop: exit main ENDP END main的另一个选项：

foldLeft

Answer 2

递归（但不是尾递归）解决方案：

val l = List("P ", "PP ", "PP ", "PP ", "P ", "PP ", "PP ", "P ")

def splitBy(l: List[String], s: String): List[List[String]] = {
  l.splitAt(l.lastIndexOf(s)) match {
    case (Nil, tail) => List(tail)
    case (head, tail) => splitBy(head, s) :+ tail
  }
}

splitBy(l, "P ") // List(List(P , PP , PP , PP ), List(P , PP , PP ), List(P ))

Tail Recursive version：

val l = List("P", "PP", "PP", "PP", "P", "PP", "PP", "P")

def splitBy(result: List[List[String]], l: List[String], s: String): List[List[String]] = {
  l.splitAt(l.lastIndexOf(s)) match {
    case (Nil, y) => List(y) ::: result
    case (x, y)   => splitBy(List(y) ::: result, x, s)
  }
}

println(splitBy(Nil, l, "P"))

Scala：将列表拆分为子列表

3 个答案: