binarySearch.java

// binarySearch.java
// demonstrates recursive binary search
// to run this program: C>java BinarySearchApp
////////////////////////////////////////////////////////////////
class ordArray
   {
   private long[] a;                 // ref to array a
   private int nElems;               // number of data items
   //-----------------------------------------------------------
   public ordArray(int max)          // constructor
      {
      a = new long[max];             // create array
      nElems = 0;
      }
   //-----------------------------------------------------------
   public int size()
      { return nElems; }
   //-----------------------------------------------------------
   public int find(long searchKey)
      {
      return recFind(searchKey, 0, nElems-1);
      }
   //-----------------------------------------------------------
   private int recFind(long searchKey, int lowerBound,
                                         int upperBound)
      {
      int curIn;

      curIn = (lowerBound + upperBound ) / 2;
      if(a[curIn]==searchKey)
         return curIn;              // found it
      else if(lowerBound > upperBound)
         return nElems;             // can't find it
      else                          // divide range
         {
         if(a[curIn] < searchKey)   // it's in upper half
            return recFind(searchKey, curIn+1, upperBound);
         else                       // it's in lower half
            return recFind(searchKey, lowerBound, curIn-1);
         }  // end else divide range
      }  // end recFind()
   //-----------------------------------------------------------
   public void insert(long value)    // put element into array
      {
      int j;
      for(j=0; j<nElems; j++)        // find where it goes
         if(a[j] > value)            // (linear search)
            break;
      for(int k=nElems; k>j; k--)    // move bigger ones up
         a[k] = a[k-1];
      a[j] = value;                  // insert it
      nElems++;                      // increment size
      }  // end insert()
   //-----------------------------------------------------------
   public void display()             // displays array contents
      {
      for(int j=0; j<nElems; j++)       // for each element,
         System.out.print(a[j] + " ");  // display it
      System.out.println("");
      }
   //-----------------------------------------------------------
   }  // end class ordArray
////////////////////////////////////////////////////////////////
class BinarySearchApp
   {
   public static void main(String[] args)
      {
      int maxSize = 100;             // array size
      ordArray arr;                  // reference to array
      arr = new ordArray(maxSize);   // create the array

      arr.insert(72);                // insert items
      arr.insert(90);
      arr.insert(45);
      arr.insert(126);
      arr.insert(54);
      arr.insert(99);
      arr.insert(144);
      arr.insert(27);
      arr.insert(135);
      arr.insert(81);
      arr.insert(18);
      arr.insert(108);
      arr.insert(9);
      arr.insert(117);
      arr.insert(63);
      arr.insert(36);

      arr.display();                 // display array

      int searchKey = 27;            // search for item
      if( arr.find(searchKey) != arr.size() )
         System.out.println("Found " + searchKey);
      else
         System.out.println("Can't find " + searchKey);
      }  // end main()
   }  // end class BinarySearchApp
////////////////////////////////////////////////////////////////