Implements a Bottom-up Mergesort, without recursion. - Java Data Structure

Java examples for Data Structure:Sort

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Description

Implements a Bottom-up Mergesort, without recursion.

Demo Code



class MergeBU {/*ww  w  .j a  va 2 s  .  com*/

  private static Comparable[] comparable;

  private static boolean less(Comparable v, Comparable w) {
    return v.compareTo(w) < 0;
  }

  public static boolean isSorted(Comparable[] a) {
    for (int i = 1; i < a.length; i++)
      if (less(a[i], a[i - 1]))
        return false;

    return true;
  }

  private static void merge(Comparable[] a, int lo, int mid, int hi) {
    // copy the array
    for (int k = lo; k <= hi; k++)
      comparable[k] = a[k];

    int i = lo, j = mid + 1;

    for (int k = lo; k <= hi; k++) {
      if (i > mid)
        a[k] = comparable[j++];
      else if (j > hi)
        a[k] = comparable[i++];
      else if (less(comparable[j], comparable[i]))
        a[k] = comparable[j++];
      else
        a[k] = comparable[i++];
    }
  }

  public static void sort(Comparable[] a) {
    int N = a.length;
    comparable = new Comparable[N];

    for (int sz = 1; sz < N; sz = sz + sz)
      for (int lo = 0; lo < N - sz; lo += sz + sz)
        merge(a, lo, lo + sz + 1, Math.min(lo + sz + sz - 1, N - 1));
  }

  public static void main(String[] args) {
    Integer[] data = new Integer[] { 5, 1, 3, 7, 4, 8, 1, 38, 10, 9, 8, 44 };
    sort(data);

    System.out.print("Array sorted by Bottom-up Mergesort: ");
    for (Integer x : data) {
      System.out.printf("%s ", x);
    }
  }
}

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