Scala example source code file (Sorting.scala)

This example Scala source code file (Sorting.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

array, array, big, boolean, classmanifest, classmanifest, int, int, k, mid-size, ordering, ordering, seq, small

The Scala Sorting.scala source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2006-2009, Ross Judson           **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala.util

import scala.reflect.ClassManifest
import scala.math.Ordering

/** The Sorting object provides functions that can sort various kinds of
  * objects. You can provide a comparison function, or you can request a sort
  * of items that are viewable as <code>Ordered. Some sorts that
  * operate directly on a subset of value types are also provided. These
  * implementations are derived from those in the Sun JDK.
  *
  * Note that stability doesn't matter for value types, so use the quickSort
  * variants for those. <code>stableSort is intended to be used with
  * objects when the prior ordering should be preserved, where possible.
  *
  * @author  Ross Judson
  * @version 1.0
  */
object Sorting {
  /** Quickly sort an array of Doubles. */
  def quickSort(a: Array[Double]) { sort1(a, 0, a.length) }

  /** Quickly sort an array of items with an implicit Ordering. */
  def quickSort[K: Ordering](a: Array[K]) { sort1(a, 0, a.length) }

  /** Quickly sort an array of Ints. */
  def quickSort(a: Array[Int]) { sort1(a, 0, a.length) }

  /** Quickly sort an array of Floats. */
  def quickSort(a: Array[Float]) { sort1(a, 0, a.length) }

  /** Sort an array of K where K is Ordered, preserving the existing order
    * where the values are equal. */      
  def stableSort[K: ClassManifest: Ordering](a: Array[K]) {
    stableSort(a, 0, a.length-1, new Array[K](a.length), Ordering[K].lt _)
  }

  /** Sorts an array of <code>K given an ordering function
   *  <code>f. f should return true iff
   *  its first parameter is strictly less than its second parameter.
   */
  def stableSort[K: ClassManifest](a: Array[K], f: (K, K) => Boolean) {
    stableSort(a, 0, a.length-1, new Array[K](a.length), f)
  }

  /** Sorts an arbitrary sequence into an array, given a comparison function
   *  that should return <code>true iff parameter one is strictly less
   *  than parameter two.
   *
   *  @param  a the sequence to be sorted.
   *  @param  f the comparison function.
   *  @return the sorted sequence of items.
   */
  def stableSort[K: ClassManifest](a: Seq[K], f: (K, K) => Boolean): Array[K] = {
    val ret = a.toArray
    stableSort(ret, f)
    ret
  }

  /** Sorts an arbitrary sequence of items that are viewable as ordered. */
  def stableSort[K: ClassManifest: Ordering](a: Seq[K]): Array[K] =
    stableSort(a, Ordering[K].lt _)

  /** Stably sorts a sequence of items given an extraction function that will
   *  return an ordered key from an item.
   *
   *  @param  a the sequence to be sorted.
   *  @param  f the comparison function.
   *  @return the sorted sequence of items.
   */
  def stableSort[K: ClassManifest, M: Ordering](a: Seq[K], f: K => M): Array[K] =
    stableSort(a)(implicitly[ClassManifest[K]], Ordering[M] on f)

  private def sort1[K: Ordering](x: Array[K], off: Int, len: Int) {
    val ord = Ordering[K]
    import ord._

    def swap(a: Int, b: Int) {
      val t = x(a)
      x(a) = x(b)
      x(b) = t
    }
    def vecswap(_a: Int, _b: Int, n: Int) {
      var a = _a
      var b = _b
      var i = 0
      while (i < n) {
        swap(a, b)
        i += 1
        a += 1
        b += 1
      }
    }
    def med3(a: Int, b: Int, c: Int) = {
      if (x(a) < x(b)) {
        if (x(b) < x(c)) b else if (x(a) < x(c)) c else a
      } else {
        if (x(b) > x(c)) b else if (x(a) > x(c)) c else a
      }
    }
    def sort2(off: Int, len: Int) {
      // Insertion sort on smallest arrays
      if (len < 7) {
        var i = off
        while (i < len + off) {
          var j = i
          while (j > off && x(j-1) > x(j)) {
            swap(j, j-1)
            j -= 1
          }
          i += 1
        }
      } else {
        // Choose a partition element, v
        var m = off + (len >> 1)        // Small arrays, middle element
        if (len > 7) {
          var l = off
          var n = off + len - 1
          if (len > 40) {        // Big arrays, pseudomedian of 9
            var s = len / 8
            l = med3(l, l+s, l+2*s)
            m = med3(m-s, m, m+s)
            n = med3(n-2*s, n-s, n)
          }
          m = med3(l, m, n) // Mid-size, med of 3
        }
        val v = x(m)

        // Establish Invariant: v* (<v)* (>v)* v*
        var a = off
        var b = a
        var c = off + len - 1
        var d = c
        var done = false
        while (!done) {
          while (b <= c && x(b) <= v) {
            if (x(b) == v) {
              swap(a, b)
              a += 1
            }
            b += 1
          }
          while (c >= b && x(c) >= v) {
            if (x(c) == v) {
              swap(c, d)
              d -= 1
            }
            c -= 1
          }
          if (b > c) {
            done = true
          } else {
            swap(b, c)
            c -= 1
            b += 1
          }
        }

        // Swap partition elements back to middle
        val n = off + len
        var s = math.min(a-off, b-a)
        vecswap(off, b-s, s)
        s = math.min(d-c, n-d-1)
        vecswap(b,   n-s, s)

        // Recursively sort non-partition-elements
        s = b - a
        if (s > 1)
          sort2(off, s)
        s = d - c
        if (s > 1)
          sort2(n-s, s)
      }
    }
    sort2(off, len)
  }

  private def sort1(x: Array[Int], off: Int, len: Int) {
    def swap(a: Int, b: Int) {
      val t = x(a)
      x(a) = x(b)
      x(b) = t
    }
    def vecswap(_a: Int, _b: Int, n: Int) {
      var a = _a
      var b = _b
      var i = 0
      while (i < n) {
        swap(a, b)
        i += 1
        a += 1
        b += 1
      }
    }
    def med3(a: Int, b: Int, c: Int) = {
      if (x(a) < x(b)) {
        if (x(b) < x(c)) b else if (x(a) < x(c)) c else a
      } else {
        if (x(b) > x(c)) b else if (x(a) > x(c)) c else a
      }
    }
    def sort2(off: Int, len: Int) {
      // Insertion sort on smallest arrays
      if (len < 7) {
        var i = off
        while (i < len + off) {
          var j = i
          while (j>off && x(j-1) > x(j)) {
            swap(j, j-1)
            j -= 1
          }
          i += 1
        }
      } else {
        // Choose a partition element, v
        var m = off + (len >> 1)        // Small arrays, middle element
        if (len > 7) {
          var l = off
          var n = off + len - 1
          if (len > 40) {        // Big arrays, pseudomedian of 9
            var s = len / 8
            l = med3(l, l+s, l+2*s)
            m = med3(m-s, m, m+s)
            n = med3(n-2*s, n-s, n)
          }
          m = med3(l, m, n) // Mid-size, med of 3
        }
        val v = x(m)

        // Establish Invariant: v* (<v)* (>v)* v*
        var a = off
        var b = a
        var c = off + len - 1
        var d = c
        var done = false
        while (!done) {
          while (b <= c && x(b) <= v) {
            if (x(b) == v) {
              swap(a, b)
              a += 1
            }
            b += 1
          }
          while (c >= b && x(c) >= v) {
            if (x(c) == v) {
              swap(c, d)
              d -= 1
            }
            c -= 1
          }
          if (b > c) {
            done = true
          } else {
            swap(b, c)
            c -= 1
            b += 1
          }
        }

        // Swap partition elements back to middle
        val n = off + len
        var s = math.min(a-off, b-a)
        vecswap(off, b-s, s)
        s = math.min(d-c, n-d-1)
        vecswap(b,   n-s, s)

        // Recursively sort non-partition-elements
        s = b - a
        if (s > 1)
          sort2(off, s)
        s = d - c
        if (s > 1)
          sort2(n-s, s)
      }
    }
    sort2(off, len)
  }

  private def sort1(x: Array[Double], off: Int, len: Int) {
    def swap(a: Int, b: Int) {
      val t = x(a)
      x(a) = x(b)
      x(b) = t
    }
    def vecswap(_a: Int, _b: Int, n: Int) {
      var a = _a
      var b = _b
      var i = 0
      while (i < n) {
        swap(a, b)
        i += 1
        a += 1
        b += 1
      }
    }
    def med3(a: Int, b: Int, c: Int) = {
      val ab = x(a) compare x(b)
      val bc = x(b) compare x(c)
      val ac = x(a) compare x(c)
      if (ab < 0) {
        if (bc < 0) b else if (ac < 0) c else a
      } else {
        if (bc > 0) b else if (ac > 0) c else a
      }
    }
    def sort2(off: Int, len: Int) {
      // Insertion sort on smallest arrays
      if (len < 7) {
        var i = off
        while (i < len + off) {
          var j = i
          while (j > off && (x(j-1) compare x(j)) > 0) {
            swap(j, j-1)
            j -= 1
          }
          i += 1
        }
      } else {
        // Choose a partition element, v
        var m = off + (len >> 1)        // Small arrays, middle element
        if (len > 7) {
          var l = off
          var n = off + len - 1
          if (len > 40) {        // Big arrays, pseudomedian of 9
            var s = len / 8
            l = med3(l, l+s, l+2*s)
            m = med3(m-s, m, m+s)
            n = med3(n-2*s, n-s, n)
          }
          m = med3(l, m, n) // Mid-size, med of 3
        }
        val v = x(m)

        // Establish Invariant: v* (<v)* (>v)* v*
        var a = off
        var b = a
        var c = off + len - 1
        var d = c
        var done = false
        while (!done) {
          var bv = x(b) compare v
          while (b <= c && bv <= 0) {
            if (bv == 0) {
              swap(a, b)
              a += 1
            }
            b += 1
            if (b <= c) bv = x(b) compare v
          }
          var cv = x(c) compare v
          while (c >= b && cv >= 0) {
            if (cv == 0) {
              swap(c, d)
              d -= 1
            }
            c -= 1
            if (c >= b) cv = x(c) compare v
          }
          if (b > c) {
            done = true
          } else {
            swap(b, c)
            c -= 1
            b += 1
          }
        }

        // Swap partition elements back to middle
        val n = off + len
        var s = math.min(a-off, b-a)
        vecswap(off, b-s, s)
        s = math.min(d-c, n-d-1)
        vecswap(b,   n-s, s)

        // Recursively sort non-partition-elements
        s = b - a
        if (s > 1)
          sort2(off, s)
        s = d - c
        if (s > 1)
          sort2(n-s, s)
      }
    }
    sort2(off, len)
  }

  private def sort1(x: Array[Float], off: Int, len: Int) {
    def swap(a: Int, b: Int) {
      val t = x(a)
      x(a) = x(b)
      x(b) = t
    }
    def vecswap(_a: Int, _b: Int, n: Int) {
      var a = _a
      var b = _b
      var i = 0
      while (i < n) {
        swap(a, b)
        i += 1
        a += 1
        b += 1
      }
    }
    def med3(a: Int, b: Int, c: Int) = {
      val ab = x(a) compare x(b)
      val bc = x(b) compare x(c)
      val ac = x(a) compare x(c)
      if (ab < 0) {
        if (bc < 0) b else if (ac < 0) c else a
      } else {
        if (bc > 0) b else if (ac > 0) c else a
      }
    }
    def sort2(off: Int, len: Int) {
      // Insertion sort on smallest arrays
      if (len < 7) {
        var i = off
        while (i < len + off) {
          var j = i
          while (j > off && (x(j-1) compare x(j)) > 0) {
            swap(j, j-1)
            j -= 1
          }
          i += 1
        }
      } else {
        // Choose a partition element, v
        var m = off + (len >> 1)        // Small arrays, middle element
        if (len > 7) {
          var l = off
          var n = off + len - 1
          if (len > 40) {        // Big arrays, pseudomedian of 9
            var s = len / 8
            l = med3(l, l+s, l+2*s)
            m = med3(m-s, m, m+s)
            n = med3(n-2*s, n-s, n)
          }
          m = med3(l, m, n) // Mid-size, med of 3
        }
        val v = x(m)

        // Establish Invariant: v* (<v)* (>v)* v*
        var a = off
        var b = a
        var c = off + len - 1
        var d = c
        var done = false
        while (!done) {
          var bv = x(b) compare v
          while (b <= c && bv <= 0) {
            if (bv == 0) {
              swap(a, b)
              a += 1
            }
            b += 1
            if (b <= c) bv = x(b) compare v
          }
          var cv = x(c) compare v
          while (c >= b && cv >= 0) {
            if (cv == 0) {
              swap(c, d)
              d -= 1
            }
            c -= 1
            if (c >= b) cv = x(c) compare v
          }
          if (b > c) {
            done = true
          } else {
            swap(b, c)
            c -= 1
            b += 1
          }
        }

        // Swap partition elements back to middle
        val n = off + len
        var s = math.min(a-off, b-a)
        vecswap(off, b-s, s)
        s = math.min(d-c, n-d-1)
        vecswap(b,   n-s, s)

        // Recursively sort non-partition-elements
        s = b - a
        if (s > 1)
          sort2(off, s)
        s = d - c
        if (s > 1)
          sort2(n-s, s)
      }
    }
    sort2(off, len)
  }

  private def stableSort[K : ClassManifest](a: Array[K], lo: Int, hi: Int, scratch: Array[K], f: (K,K) => Boolean) {
    if (lo < hi) {
      val mid = (lo+hi) / 2
      stableSort(a, lo, mid, scratch, f)
      stableSort(a, mid+1, hi, scratch, f)
      var k, t_lo = lo
      var t_hi = mid + 1
      while (k <= hi) {
        if ((t_lo <= mid) && ((t_hi > hi) || (!f(a(t_hi), a(t_lo))))) { 
          scratch(k) = a(t_lo) 
          t_lo += 1 
        } else { 
          scratch(k) = a(t_hi) 
          t_hi += 1 
        }
        k += 1
      }
      k = lo
      while (k <= hi) {
        a(k) = scratch(k)
        k += 1
      }
    }
  }
}