java codility training Genomic-range-query

Question

The task is:

A non-empty zero-indexed string S is given. String S consists of N characters from the set of upper-case English letters A, C, G, T.

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Answer 1

scala solution 100/100

import scala.annotation.switch
import scala.collection.mutable

object Solution {
  def solution(s: String, p: Array[Int], q: Array[Int]): Array[Int] = {

    val n = s.length

    def arr = mutable.ArrayBuffer.fill(n + 1)(0L)

    val a = arr
    val c = arr
    val g = arr
    val t = arr

    for (i <- 1 to n) {
      def inc(z: mutable.ArrayBuffer[Long]): Unit = z(i) = z(i - 1) + 1L

      def shift(z: mutable.ArrayBuffer[Long]): Unit = z(i) = z(i - 1)

      val char = s(i - 1)
      (char: @switch) match {
        case 'A' => inc(a); shift(c); shift(g); shift(t);
        case 'C' => shift(a); inc(c); shift(g); shift(t);
        case 'G' => shift(a); shift(c); inc(g); shift(t);
        case 'T' => shift(a); shift(c); shift(g); inc(t);
      }
    }

    val r = mutable.ArrayBuffer.fill(p.length)(0)

    for (i <- p.indices) {
      val start = p(i)
      val end = q(i) + 1
      r(i) =
        if (a(start) != a(end)) 1
        else if (c(start) != c(end)) 2
        else if (g(start) != g(end)) 3
        else if (t(start) != t(end)) 4
        else 0
    }

    r.toArray
  }
}