C++ Tutorial/STL Algorithms Binary search/binary search

Binary search after sorting

<source lang="cpp">#include <iostream>

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

using namespace std; bool greater10( int value ); int main() {

  const int SIZE = 10;
  int a[ SIZE ] = { 10, 2, 17, 5, 16, 8, 13, 11, 20, 7 };
  vector< int > v( a, a + SIZE );
  
  vector< int >::iterator location;
  location = find( v.begin(), v.end(), 16 );
  sort( v.begin(), v.end() );
  if ( binary_search( v.begin(), v.end(), 13 ) )
     cout << "\n\n13 was found in v";
  else
     cout << "\n\n13 was not found in v";
  return 0;

} bool greater10( int value ) { return value > 10; }</source>

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;
   }

}</source>

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

Illustrating the generic binary search algorithms

<source lang="cpp">#include <iostream>

1. include <cassert>
2. include <algorithm>
3. 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;

}</source>

1 0

Use binary_search() to binary search a vector

<source lang="cpp">#include <algorithm>

1. include <vector>
2. include <string>
3. include <iostream>

using namespace std; typedef vector <string> VECTOR_STRINGS; int main () {

   VECTOR_STRINGS v;
   v.push_back ("A");
   v.push_back ("B");
   v.push_back ("C");
   v.push_back ("D");
   // insert a duplicate into the vector
   v.push_back ("D");
   for (size_t nItem = 0; nItem < v.size (); ++ nItem){
       cout << "Name [" << nItem << "] = \"";
       cout << v [nItem] << "\"" << endl;
   }
   // sort the names using std::sort
   sort (v.begin (), v.end ());
   for (size_t nItem = 0; nItem < v.size (); ++ nItem){
       cout << "Name [" << nItem << "] = \"";
       cout << v [nItem] << "\"" << endl;
   }
   bool bElementFound = binary_search (v.begin (), v.end (),"C");
   if (bElementFound)
       cout << "Result: C was found in the vector!" << endl;
   else
       cout << "Element not found " << endl;
   return 0;

}</source>

Use binary_search to locate a value in a vector

<source lang="cpp">#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;

}</source>

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