C++ Tutorial/STL Algorithms Non modifying sequence operations/adjacent find

adjacent_find: search first two elements for which the second has double the value of the first

<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>

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;
  }

}</source>

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

adjacent_find: search first two elements with equal value

<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>

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: ");
  // search first two elements with equal value
  vector<int>::iterator pos;
  pos = adjacent_find (coll.begin(), coll.end());
  if (pos != coll.end()) {
      cout << "first two elements with equal value have position "
           << distance(coll.begin(),pos) + 1
           << endl;
  }

}</source>

coll: 1 3 2 4 5 5 0
first two elements with equal value have position 5

Illustrating the generic adjacent_find algorithm

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

1. include <string>
2. include <algorithm>
3. include <cassert>
4. include <functional>
5. include <deque>

using namespace std; int main() {

 deque<string> player(5);
 deque<string>::iterator i;
 player[0] = "PPPP";
 player[1] = "AAAAAA";
 player[2] = "AAAAAA";
 player[3] = "NNNNNNNN";
 player[4] = "RRRRRRRRR";
 // Find the first pair of equal consecutive names:
 i = adjacent_find(player.begin(), player.end());
 cout << *i;
 return 0;

}</source>

AAAAAA"

Use generic adjacent_find algorithm with a predicate to find the first name that is lexicographically greater than the next one

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

1. include <string>
2. include <algorithm>
3. include <cassert>
4. include <functional>
5. include <deque>

using namespace std; int main() {

 deque<string> player(5);
 deque<string>::iterator i;
 player[0] = "PPPP";
 player[1] = "AAAAAA";
 player[2] = "AAAAAA";
 player[3] = "NNNNNNNN";
 player[4] = "RRRRRRRRR";
 
 i = adjacent_find(player.begin(), player.end(), greater<string>());
 cout << *i << endl;
 return 0;

}</source>

PPPP