Merge-Sort Algorithm implementation in JAVA

Merge-Sort Function

void MergeSort(int low, int high)
   // a[low : high] is a global array to be sorted.
   // Small(P) is true if there is only one element to
   // sort. In this case the list is already sorted.
   {
       if (low < high) { // If there are more than one element
              // Divide P into subproblems.
              // Find where to split the set.
              int mid = (low + high)/2;
              // Solve the subproblems.
              MergeSort(low, mid);
              MergeSort(mid + 1, high);
              // Combine the solutions.
              Merge(low, mid, high);
       }
   }

   void Merge(int low, int mid, int high)
   // a[low:high] is a global array containing two sorted
   // subsets in a[low:mid] and in a[mid+1:high]. The goal
   // is to merge these two sets into a single set residing
   // in a[low:high]. b[] is an auxiliary global array.
   {
       int h = low, i = low, j = mid+1, k;
       while ((h <= mid) && (j <= high)) {
          if (a[h] <= a[j]) { b[i] = a[h]; h++; }
          else { b[i] = a[j]; j++; } i++;
       }
       if (h > mid) for (k=j; k<=high; k++) {
                       b[i] = a[k]; i++;
                    }
       else for (k=h; k<=mid; k++) {
               b[i] = a[k]; i++;
            }
       for (k=low; k<=high; k++) a[k] = b[k];
   }

Merge Sort Java Code :

import java.util.*;

public class MergeSort {
 public int a[] = new int[50];

 public void merge_sort(int low, int high) {
  int mid;
  if (low < high) {
   mid = (low + high) / 2;
   merge_sort(low, mid);
   merge_sort(mid + 1, high);
   merge(low, mid, high);
  }
 }

 public void merge(int low, int mid, int high) {
  int h, i, j, k;
  int b[] = new int[50];
  h = low;
  i = low;
  j = mid + 1;

  while ((h <= mid) && (j <= high)) {
   if (a[h] <= a[j]) {
    b[i] = a[h];
    h++;
   } else {
    b[i] = a[j];
    j++;
   }
   i++;
  }
  if (h > mid) {
   for (k = j; k <= high; k++) {
    b[i] = a[k];
    i++;
   }
  } else {
   for (k = h; k <= mid; k++) {
    b[i] = a[k];
    i++;
   }
  }
  for (k = low; k <= high; k++)
   a[k] = b[k];
 }

 public MergeSort() {
  int num, i;

  System.out.println("             MERGE SORT PROGRAM            ");

  System.out.println();
  System.out.println();
  System.out
    .println("Please Enter THE No. OF ELEMENTS you want to sort[THEN PRESS ENTER]:");
  num = new Scanner(System.in).nextInt();
  System.out.println();
  System.out.println("Now, Please Enter the (" + num
    + ") nos. [THEN PRESS ENTER]:");
  for (i = 1; i <= num; i++) {
   a[i] = new Scanner(System.in).nextInt();
  }
  merge_sort(1, num);
  System.out.println();
  System.out.println("So, the sorted list (using MERGE SORT) will be :");
  System.out.println();
  System.out.println();

  for (i = 1; i <= num; i++)
   System.out.print(a[i] + "    ");

 }

 public static void main(String[] args) {
  new MergeSort();
 }
}

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Implementation of a basic generic tree, with labels of type T - Data Structure

// This implements a basic generic tree, with labels of type T,
// pointer to the parent node, and a singly linked list of children nodes.

class Tree<T>  {
    private T label;
    private Tree<T> parent;
    private Tree<T> nextSibling; // next node on the list of parents's 
                                 //  children
    private Tree<T> firstChild;  // first in the linked list of children

                                 
//  Getters and setters
    public T getLabel() { return label; }  
    public void setLabel(T v) { label = v; }
    public Tree<T> getParent() { return parent;}
    public Tree<T> getNextSibling() { return nextSibling;}
    public Tree<T> getFirstChild() { return firstChild;}

// Add C to the front of the children of this
    public void addChild(Tree<T> c) {
         c.parent = this;
         if (firstChild == null) 
           firstChild = c;
         else {
             c.nextSibling = firstChild;
             firstChild = c;
            }
    }

// Check if the node is a leaf
    public boolean Leaf() { return firstChild==null; }

// `Convert the tree into a string. The structure is indicated by
// square brackets. Uses a preorder listing.
    public String toString() {
       String S = "[ " + label.toString();
       Tree<T> N = firstChild;
       while (N != null) {
          S = S + " " + N.toString();
          N = N.nextSibling;
        }
       return S+" ]";
     }

     public void displayPreorder() {
         displayPreorder1(0); }

     public void displayPreorder1(int Indent) {
         for (int I = 0; I < Indent; I++) System.out.print(" ");
         System.out.println(label.toString());
         Tree<T> N = firstChild;
         while (N != null) { 
            N.displayPreorder1(Indent+3);
            N = N.nextSibling;
           }
         }

     public void displayPostorder() {
         displayPostorder1(0); }

     public void displayPostorder1(int Indent) {
         Tree<T> N = firstChild;
         while (N != null) { 
            N.displayPostorder1(Indent+3);
            N = N.nextSibling;
           }
         for (int I = 0; I < Indent; I++) System.out.print(" ");
         System.out.println(label.toString());
         }
}

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Stack implemented as array - Data Structure

// Stack implemented as array
public class ArrayStack<T> {
     private T[] stack;
     private int numElements = 0; // points to slot after top element

     public ArrayStack(T[] s) { stack = s; }  

     public boolean emptyStack() { 
         return numElements == 0; }
   
     public T  top() {
         return stack[numElements-1];
       }

     public void push(T x) {
         stack[numElements] = x;
         numElements++;
       }
  
     public T pop() {
         numElements--;
         return stack[numElements];
      }

    public static void main(String[] args) {
       ArrayStack<Integer> s = new ArrayStack<Integer>(new Integer[100]);
       s.push(2);
       s.push(3);
       s.push(5);
       System.out.println(s.top());
       System.out.println(s.pop());
       System.out.println(s.pop());
       s.push(15);
       s.push(22);
       System.out.println(s.pop());
   }
}

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Singly linked list with header - Data Structure

class OrderedList  {
   private int value;
   private OrderedList next;

// Note: No setValue() method or setNext() methods are provided, 
// since those could require reordering the list.
  
   public int getValue() {
       return value; }

   public OrderedList getNext() {
       return next; }

// If X is in the list, returns the previous node.
// If X is not in the list, returns the node for the greatest element less 
// than  X.

   public OrderedList searchBefore(int x) { // Locate node containing X
       OrderedList n = this;
       while (true) {
          if (n.next==null) return n;
          if (n.next.value >= x) return n;
          n = n.next;
         } 
      }

// Is element x in the list. Note the use of the left to right evaluation of 
// && (if the condition n.net != null is false, then the conjunction returns
// false without evaluating n.next.value=x.

   public boolean inList(int x) {
       OrderedList n = searchBefore(x);
       return n.next != null && n.next.value == x; }

// Adds x to the ordered list, if it is not already there.
   public void add(int x) {
       OrderedList n = searchBefore(x);
       if (n.next == null || n.next.value != x) {
           OrderedList newNode = new OrderedList();
           newNode.value = x;
           newNode.next = n.next;
           n.next = newNode;
         }
     }
       
// Deletes X from the ordered list, if it is there.

   public void delete(int x) {
       OrderedList n = searchBefore(x);
       if (n.next != null && n.next.value == x)
          n.next = n.next.next;
      }



   public String toString() {
          OrderedList a = next;
          String s = "[";
          while (a != null) {
             s = s + a.value + " ";
             a = a.next;
           }
         return s+ "]";
         }

   public static void main(String[] args) {
      OrderedList l = new OrderedList();
      l.add(31);
      l.add(41);
      l.add(59);
      l.add(26);
      l.add(53);
      l.add(58);
      l.add(37);
      l.delete(53);
      System.out.println(l.toString());
}
}

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Ordered array of ints with no repetition - Data Structure

public class OrderedArray {

   private int numElements = 0;
   private int[] elements;

// Constructor..Note: the caller has to provide the array of elements.
// This is because Java generics do not allow a call "elements = new T[100]".
//
   public OrderedArray(int[] elts) {
        elements = elts; }

   public int getNumElements() { return numElements; } 

   public int nth(int n) { // return the Nth element
       if (n < numElements) return elements[n]; else return -1; }
  
   public int first() { return nth(0); } 
   public int  last() { return nth(numElements-1); } 

//  search(X) returns the index where X is, if X is in the list.
//  Otherwise, it returns the index of the smallest number greater than X
   public int search(int x) {
       if (numElements==0) return 0;
       if (x <= first()) return 0;
       if (x > last()) return numElements;
       if (x == last()) return numElements-1;
       return search1(x,0,numElements-1); 
     }

// X is strictly between L and U.
   public int search1(int x,int l,int u) {
        if (u==l+1) return u;
        else {
           int m = (l+u)/2;
           if (x==elements[m]) return m;
           else if (x < elements[m]) return  search1(x,l,m);
           else return search1(x,m,u);
        }
     }

   public boolean inList(int x) {
       return (elements[search(x)]==x); }

   public void add(int x) {
      int i = search(x);
      if (elements[i] != x)  {
        for (int j = numElements; j>i; j--)
           elements[j]=elements[j-1];
        elements[i]=x;
        numElements++;
       }
     }

   public void delete(int x) {
      int i = search(x);
      if (elements[i] == x) {
        for (int j=i+1; j < numElements; j++)
          elements[j-1] = elements[j];
        numElements--;
      }
    }


   public String toString() {
      String s = "[";
      for (int i=0; i < numElements; i++)
         s = s + " " + elements[i];
      return s+"]";
   }

   public static void main(String[] args) {
      OrderedArray l = new OrderedArray(new int[100]);
      l.add(31);
      l.add(41);
      l.add(59);
      l.add(26);
      l.add(53);
      l.add(58);
      l.add(37);
      l.delete(53);
      System.out.println(l.toString());
      System.out.println(l.search(2));
      System.out.println(l.search(26));
      System.out.println(l.search(53));
      System.out.println(l.search(54));
      System.out.println(l.search(195));
}
}

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Stop Watch Program - To measure the amount of time to process each input

public class Stopwatch { 

    private final long start;

    public Stopwatch() {
        start = System.currentTimeMillis();
    } 

    // return time (in seconds) since this object was created
    public double elapsedTime() {
        long now = System.currentTimeMillis();
        return (now - start) / 1000.0;
    } 

}

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