C++/STL Algorithms Binary search/binary search

binary_search a list

<source lang="cpp">

/* The following code example is taken from the book

* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/

1. include <iostream>
2. include <vector>
3. include <deque>
4. include <list>
5. include <set>
6. include <map>
7. include <string>
8. include <algorithm>
9. include <iterator>
10. include <functional>
11. include <numeric>

/* PRINT_ELEMENTS()

* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/

template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {

   typename T::const_iterator pos;
   std::cout << optcstr;
   for (pos=coll.begin(); pos!=coll.end(); ++pos) {
       std::cout << *pos << " ";
   }
   std::cout << std::endl;

} /* INSERT_ELEMENTS (collection, first, last)

* - fill values from first to last into the collection
* - NOTE: NO half-open range
*/

template <class T> inline void INSERT_ELEMENTS (T& coll, int first, int last) {

   for (int i=first; i<=last; ++i) {
       coll.insert(coll.end(),i);
   }

}

using namespace std; int main() {

   list<int> coll;
   INSERT_ELEMENTS(coll,1,9);
   PRINT_ELEMENTS(coll);
   // check existence of element with value 5
   if (binary_search(coll.begin(), coll.end(), 5)) {
       cout << "5 is present" << endl;
   }
   else {
       cout << "5 is not present" << endl;
   }
   // check existence of element with value 42
   if (binary_search(coll.begin(), coll.end(), 42)) {
       cout << "42 is present" << endl;
   }
   else {
       cout << "42 is not present" << endl;
   }

} /* 1 2 3 4 5 6 7 8 9 5 is present 42 is not present

*/        
 </source>

Illustrating the generic binary search algorithms

<source lang="cpp">

1. include <iostream>
2. include <cassert>
3. include <algorithm>
4. include <vector>

using namespace std; int main() {

 vector<int> v(5);
 bool found;
 for (int i = 0; i < 5; ++i)
    v[i] = i;
 found = binary_search(v.begin(), v.end(), 3);
 cout << found << " ";
 // Try searching for a value that"s not present:
 found = binary_search (v.begin(), v.end(), 9);
 cout << found;
 return 0;

} /* 1 0

*/        
 </source>

Use binary_search to locate a value in a vector

<source lang="cpp">

1. include <iostream>

using std::cout; using std::endl;

1. include <algorithm>
2. include <vector>
3. include <iterator>

int main() {

  int a[ 10 ] = { 10, 2, 17, 5, 16, 8, 13, 11, 20, 7 };
  std::vector< int > v( a, a + 10 ); // copy of a
  std::ostream_iterator< int > output( cout, " " );
  cout << "Vector v contains: ";
  std::copy( v.begin(), v.end(), output ); // display output vector
  // locate first occurrence of 16 in v
  std::vector< int >::iterator location;
  // use binary_search to locate 13 in v
  if ( std::binary_search( v.begin(), v.end(), 13 ) )
     cout << "\n\n13 was found in v";
  else
     cout << "\n\n13 was not found in v";

  cout << endl;
  return 0;

} /* Vector v contains: 10 2 17 5 16 8 13 11 20 7 13 was not found in v

*/        
 </source>