binarysearch.cpp

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// Fig 20.3: BinarySearch.cpp
// BinarySearch class member-function definition.
#include <iostream>
using std::cout;
using std::endl;

#include <cstdlib> // prototypes for functions srand and rand
using std::rand;
using std::srand;

#include <ctime> // prototype for function time
using std::time;

#include <algorithm> // prototype for sort function
#include "BinarySearch.h" // class BinarySearch definition

// constructor initializes vector with random ints and sorts the vector
BinarySearch::BinarySearch( int vectorSize )
{
   size = ( vectorSize > 0 ? vectorSize : 10 ); // validate vectorSize
   srand( time( 0 ) ); // seed using current time

   // fill vector with random ints in range 10-99
   for ( int i = 0; i < size; i++ )
      data.push_back( 10 + rand() % 90 ); // 10-99

   std::sort( data.begin(), data.end() ); // sort the data
} // end BinarySearch constructor

// perform a binary search on the data             
int BinarySearch::binarySearch( int searchElement ) const
{
   int low = 0; // low end of the search area
   int high = size - 1; // high end of the search area
   int middle = ( low + high + 1 ) / 2; // middle element
   int location = -1; // return value; -1 if not found

   do // loop to search for element
   {
      // print remaining elements of vector to be searched
      displaySubElements( low, high );

      // output spaces for alignment
      for ( int i = 0; i < middle; i++ )
        cout << "   ";

      cout << " * " << endl; // indicate current middle

      // if the element is found at the middle
      if ( searchElement == data[ middle ] )
         location = middle; // location is the current middle
      else if ( searchElement < data[ middle ] ) // middle is too high
         high = middle - 1; // eliminate the higher half
      else // middle element is too low
         low = middle + 1; // eliminate the lower half

      middle = ( low + high + 1 ) / 2; // recalculate the middle
   } while ( ( low <= high ) && ( location == -1 ) );

   return location; // return location of search key
} // end function binarySearch

// display values in vector
void BinarySearch::displayElements() const
{
   displaySubElements( 0, size - 1 );
} // end function displayElements 

// display certain values in vector
void BinarySearch::displaySubElements( int low, int high ) const
{
   for ( int i = 0; i < low; i++ ) // output spaces for alignment
      cout << "   ";

   for ( int i = low; i <= high; i++ ) // output elements left in vector
      cout << data[ i ] << " ";

   cout << endl;
} // end function displaySubElements


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