Lecture6.scala

package week2

object Lecture6 extends App {
  def reduceSeg1[A](inp: Array[A], left: Int, right: Int, a0: A, f: (A, A) => A): A = {
    var a = a0
    var i = left
    while (i < right) {
      a = f(a, inp(i))
      i += 1
    }
    a
  }

  def mapSeg[A,B](inp: Array[A], left: Int, right: Int, fi : (Int, A) => B, out: Array[B]): Unit = {
    var i = left
    while (i < right) {
      out(i) = fi(i, inp(i))
      i += 1
    }
  }

  def scanLeft[A](inp: Array[A], a0: A, f: (A, A) => A, out: Array[A]): Unit = {
    def fi(i: Int, an: A) = {
      reduceSeg1(inp, 0, i, a0, f)
    }
    mapSeg(inp, 0, inp.length, fi, out)
    val last = inp.length - 1
    out(last + 1) = f(out(last), inp(last))
  }

  val inp = Array(1, 3, 8)
  val out = new Array[Int](4)
  scanLeft[Int](inp, 100, _+_, out)

  println(out.toList)
}