adjacent_find: search first two elements for which the second has double the value of the first : adjacent_find « STL Algorithms Non modifying sequence operations « C++ Tutorial

1. C++ Tutorial
2. STL Algorithms Non modifying sequence operations
3. adjacent_find

/* 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.
 */

#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>

using namespace std;

/* 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);
    }
}



// return whether the second object has double the value of the first
bool doubled (int elem1, int elem2)
{
   return elem1 * 2 == elem2;
}

int main()
{
   vector<int> coll;

   coll.push_back(1);
   coll.push_back(3);
   coll.push_back(2);
   coll.push_back(4);
   coll.push_back(5);
   coll.push_back(5);
   coll.push_back(0);

   PRINT_ELEMENTS(coll,"coll: ");

   vector<int>::iterator pos;
   // search first two elements for which the second has double the value of the first
   pos = adjacent_find (coll.begin(), coll.end(),   // range
                        doubled);                   // criterion

   if (pos != coll.end()) {
       cout << "first two elements with second value twice the "
            << "first have pos. "
            << distance(coll.begin(),pos) + 1
            << endl;
   }


}

coll: 1 3 2 4 5 5 0
first two elements with second value twice the first have pos. 3