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MODULE 36a_1

THE C++ STL ALGORITHM PART 13

My Training Period: xx hours

This is a continuation from previous Module, more code samples, compiled usingMicrosoft Visual C++ .Net, win32 empty console mode application. g++ compilation examples given at the end of this Module. Source code for this tutorial is available inC++ STL Algorithm source code.

• The sorted source ranges referenced must be valid; all pointers must be de-referenceable and within each sequence the last position must be reachable from the first by incrementation.

• The destination range should not overlap either of the source ranges and should be large enough to contain the destination range.

• The sorted source ranges must each be arranged as a precondition to the application of the set_difference() algorithm in accordance with the same ordering as is to be used by the algorithm to sort the combined ranges.

• The operation is stable as the relative order of elements within each range is preserved in the destination range. The source ranges are not modified by the algorithm merge.

• The value types of the input iterators need be less-than-comparable to be ordered, so that, given two elements, it may be determined either that they are equivalent, in the sense that neither is less than the other or that one is less than the other. This results in an ordering between the nonequivalent elements.

• When there are equivalent elements in both source ranges, the elements in the first range precede the elements from the second source range in the destination range.

• If the source ranges contain duplicates of an element such that there are more in the first source range than in the second, then the destination range will contain the number by which the occurrences of those elements in the first source range exceed the occurrences of those elements in the second source range.

• The complexity of the algorithm is linear with at most 2*((_Last1 – _First1) – (_Last2 – _First2)) –1 comparisons for nonempty source ranges.

// algorithm, set_difference()

#include <vector>

#include <algorithm>

// for greater<int>()

#include <functional>

#include <iostream>

using namespace std;

// return whether modulus of elem1 is less than modulus of elem2

bool mod_lesser(int elem1, int elem2)

{

   if (elem1 < 0)

      elem1 = - elem1;

   if (elem2 < 0)

      elem2 = - elem2;

   return (elem1 < elem2);

}

int main()

{

   vector <int> vec1a, vec1b, vec1(12);

   vector <int>::iterator Iter1a, Iter1b, Iter1, Result1;

   // constructing vectors vec1a & vec1b with default less-than ordering

   int i;

   for(i = -2; i <= 3; i++)

      vec1a.push_back(i);

   int j;

   for(j =-2; j <= 1; j++)

      vec1b.push_back(j);

   cout<<"Original vector vec1a with range sorted by the\nbinary predicate less than is: ";

   for(Iter1a = vec1a.begin(); Iter1a != vec1a.end(); Iter1a++)

      cout<<*Iter1a<<" ";

   cout<<endl;

   cout<<"\nOriginal vector vec1b with range sorted by the\nbinary predicate less than is: ";

   for(Iter1b = vec1b.begin(); Iter1b != vec1b.end(); Iter1b++)

      cout<<*Iter1b<<" ";

   cout<<endl;

   // constructing vectors vec2a & vec2b with ranges sorted by greater

   vector <int> vec2a(vec1a), vec2b(vec1b), vec2(vec1);

   vector <int>::iterator Iter2a, Iter2b, Iter2, Result2;

   sort(vec2a.begin(), vec2a.end(), greater<int>());

   sort(vec2b.begin(), vec2b.end(), greater<int>());

   cout<<"\nOriginal vector vec2a with range sorted by the\nbinary predicate greater is: ";

   for(Iter2a = vec2a.begin(); Iter2a != vec2a.end(); Iter2a++)

      cout<<*Iter2a<<" ";

   cout<<endl;

   cout<<"\nOriginal vector vec2b with range sorted by the\nbinary predicate greater is: ";

   for(Iter2b = vec2b.begin(); Iter2b != vec2b.end(); Iter2b++)

      cout<<*Iter2b<<" ";

   cout<<endl;

   // constructing vectors vec3a & vec3b with ranges sorted by mod_lesser

   vector <int> vec3a(vec1a), vec3b(vec1b), vec3(vec1);

   vector <int>::iterator Iter3a, Iter3b, Iter3, Result3;

   sort(vec3a.begin(), vec3a.end(), mod_lesser);

   sort(vec3b.begin(), vec3b.end(), mod_lesser);

   cout<<"\nOriginal vector vec3a with range sorted by the\nbinary predicate mod_lesser() is: ";

   for(Iter3a = vec3a.begin(); Iter3a != vec3a.end(); Iter3a++)

      cout<<*Iter3a<<" ";

   cout<<endl;

   cout<<"\nOriginal vector vec3b with range sorted by the\nbinary predicate mod_lesser() is: ";

   for(Iter3b = vec3b.begin(); Iter3b != vec3b.end(); Iter3b++)

      cout<<*Iter3b<<" ";

   cout<<endl;

   // to combine into a difference in ascending order with the default binary predicate less <int>()

   Result1 = set_difference(vec1a.begin(), vec1a.end(),

      vec1b.begin(), vec1b.end(), vec1.begin());

   cout<<"\nset_difference() of source ranges with default order,\nvector vec1mod = ";

   for(Iter1 = vec1.begin(); Iter1 != Result1; Iter1++)

      cout<<*Iter1<<" ";

   cout<<endl;

   // to combine into a difference in descending order specify binary predicate greater<int>()

   Result2 = set_difference(vec2a.begin(), vec2a.end(),

      vec2b.begin(), vec2b.end(), vec2.begin(), greater <int>());

   cout<<"\nset_difference() of source ranges with binary predicate\ngreater specified, vector vec2mod: ";

   for(Iter2 = vec2.begin(); Iter2 != Result2; Iter2++)

      cout<<*Iter2<<" ";

   cout<<endl;

   // to combine into a difference applying a user defined binary predicate mod_lesser()

   Result3 = set_difference(vec3a.begin(), vec3a.end(),

      vec3b.begin(), vec3b.end(), vec3.begin(), mod_lesser);

   cout<<"\nset_difference() of source ranges with binary predicate\nmod_lesser() specified, vector vec3mod: ";

   for(Iter3 = vec3.begin(); Iter3 != Result3; Iter3++)

      cout<<*Iter3<<" ";

   cout<<endl;

}

Output

set_intersection()

• Unites all of the elements that belong to both sorted source ranges into a single, sorted destination range, where the ordering criterion may be specified by a binary predicate.

1. template<class InputIterator1, class InputIterator2, class OutputIterator>OutputIterator set_intersection( InputIterator1 _First1, InputIterator1 _Last1, InputIterator2 _First2, InputIterator2 _Last2, OutputIterator _Result );

2. template<class InputIterator1, class InputIterator2, class OutputIterator, class BinaryPredicate>OutputIterator set_intersection( InputIterator1 _First1, InputIterator1 _Last1, InputIterator2 _First2, InputIterator2 _Last2, OutputIterator _Result, BinaryPredicate _Comp );

Parameters

// algorithm, set_intersection()

#include <vector>

#include <algorithm>

// for greater<int>()

#include <functional>

#include <iostream>

using namespace std;

// return whether modulus of elem1 is less than modulus of elem2

bool mod_lesser(int elem1, int elem2)

{

   if(elem1 < 0)

      elem1 = - elem1;

   if(elem2 < 0)

      elem2 = - elem2;

   return (elem1 < elem2);

}

int main()

{

   vector <int> vec1a, vec1b, vec1(12);

   vector <int>::iterator Iter1a, Iter1b, Iter1, Result1;

   // constructing vectors vec1a & vec1b with default less than ordering

   int i;

   for(i = -2; i <= 2; i++)

     vec1a.push_back(i);

   int j;

   for(j = -4; j <= 0; j++)

     vec1b.push_back(j);

   cout<<"Original vector vec1a with range sorted by the\nbinary predicate less than is: ";

   for(Iter1a = vec1a.begin(); Iter1a != vec1a.end(); Iter1a++)

      cout<<*Iter1a<<" ";

   cout<<endl;

   cout<<"\nOriginal vector vec1b with range sorted by the\nbinary predicate less than is: ";

   for(Iter1b = vec1b.begin(); Iter1b != vec1b.end(); Iter1b++)

      cout<<*Iter1b<<" ";

   cout<<endl;

   // constructing vectors vec2a & vec2b with ranges sorted by greater

   vector <int> vec2a(vec1a), vec2b(vec1b), vec2(vec1);

   vector <int>::iterator Iter2a, Iter2b, Iter2, Result2;

   sort(vec2a.begin(), vec2a.end(), greater<int>());

   sort(vec2b.begin(), vec2b.end(), greater<int>());

   cout<<"\nOriginal vector vec2a with range sorted by the\nbinary predicate greater is: ";

   for(Iter2a = vec2a.begin(); Iter2a != vec2a.end(); Iter2a++)

      cout<<*Iter2a<<" ";

   cout<<endl;

   cout<<"\nOriginal vector vec2b with range sorted by the\nbinary predicate greater is: ";

   for(Iter2b = vec2b.begin(); Iter2b != vec2b.end(); Iter2b++)

      cout<<*Iter2b<<" ";

   cout<<endl;

   // constructing vectors vec3a & vec3b with ranges sorted by mod_lesser

   vector<int>vec3a(vec1a), vec3b(vec1b), vec3(vec1);

   vector<int>::iterator Iter3a, Iter3b, Iter3, Result3;

   sort(vec3a.begin(), vec3a.end(), mod_lesser);

   sort(vec3b.begin(), vec3b.end(), mod_lesser);

   cout<<"\nOriginal vector vec3a with range sorted by the\nbinary predicate mod_lesser() is: ";

   for(Iter3a = vec3a.begin(); Iter3a != vec3a.end(); Iter3a++)

      cout<<*Iter3a<<" ";

   cout<<endl;

   cout<<"\nOriginal vector vec3b with range sorted by the\nbinary predicate mod_lesser() is: ";

   for(Iter3b = vec3b.begin(); Iter3b != vec3b.end(); Iter3b++)

      cout<<*Iter3b<<" ";

   cout<<endl;

   // to combine into an intersection in ascending order with the default  binary predicate less <int>()

   Result1 = set_intersection(vec1a.begin(), vec1a.end(), vec1b.begin(), vec1b.end(), vec1.begin());

   cout<<"\nset_intersection() of source ranges with default order,\nvector vec1mod: ";

   for(Iter1 = vec1.begin(); Iter1 != Result1; Iter1++)

      cout<<*Iter1<<" ";

   cout<<endl;

   // to combine into an intersection in descending order, specify binary predicate greater<int>()

   Result2 = set_intersection(vec2a.begin(), vec2a.end(), vec2b.begin(), vec2b.end(), vec2.begin(), greater<int>());

   cout<<"\nset_intersection() of source ranges with binary predicate\ngreater specified, vector vec2mod: ";

   for(Iter2 = vec2.begin(); Iter2 != Result2; Iter2++)

      cout<<*Iter2<<" ";

   cout<<endl;

   // to combine into an intersection applying a user-defined binary predicate mod_lesser

   Result3 = set_intersection(vec3a.begin(), vec3a.end(), vec3b.begin(), vec3b.end(), vec3.begin(), mod_lesser);

   cout<<"\nset_intersection() of source ranges with binary predicate\nmod_lesser() specified, vector vec3mod: ";

   for(Iter3 = vec3.begin(); Iter3 != Result3; Iter3++)

      cout<<*Iter3<<" ";

   cout<<endl;

}

Output:

• The following are program examples compiled usingg++.

// ******algorandshuffle.cpp********

// algorithm, random_shuffle() - g++

#include <vector>

#include <algorithm>

#include <functional>

#include <iostream>

using namespace std;

int main()

{

   vector <int> vec1;

   vector <int>::iterator Iter1;

   int i;

   for(i = 1; i <= 10; i++)

     vec1.push_back(i);

   cout<<"The original of vector vec1 data:\n";

   for(Iter1 = vec1.begin(); Iter1 != vec1.end(); Iter1++)

       cout<<*Iter1<<" ";

   cout<<endl;

   // random shuffle…

   random_shuffle(vec1.begin(), vec1.end());

   cout<<"The original of vector vec1 random shuffle data:\n";

   for(Iter1 = vec1.begin(); Iter1 != vec1.end(); Iter1++)

       cout<<*Iter1<<" ";

   cout<<endl;

   // shuffled once

   random_shuffle(vec1.begin(), vec1.end());

   push_heap(vec1.begin(), vec1.end());

   cout<<"Vector vec1 after reshuffle is:\n";

   for(Iter1 = vec1.begin(); Iter1 != vec1.end(); Iter1++)

       cout<<*Iter1<<" ";

   cout<<endl;

   // shuffled again

   random_shuffle(vec1.begin(), vec1.end());

   push_heap(vec1.begin(), vec1.end());

   cout<<"Vector vec1 after another reshuffle is:\n";

   for(Iter1 = vec1.begin(); Iter1 != vec1.end(); Iter1++)

       cout<<*Iter1<<" ";

   cout<<endl;

}

[bodo@bakawali ~]$ g++ algorandshuffle.cpp -o algorandshuffle

[bodo@bakawali ~]$ ./algorandshuffle

The original of vector vec1 data:

1 2 3 4 5 6 7 8 9 10

The original of vector vec1 random shuffle data:

5 4 8 9 1 6 3 2 7 10

Vector vec1 after reshuffle is:

7 1 8 9 6 4 10 3 2 5

Vector vec1 after another reshuffle is:

10 1 5 4 8 6 3 7 2 9

//*******algosearchn.cpp*********

// algorithm, search_n() - g++

// with some type conversion warning

#include <vector>

#include <list>

#include <algorithm>

#include <iostream>

using namespace std;

// return whether second element is twice the first

bool twice(int elem1, int elem2)

{    return 2 * elem1 == elem2;    }

int main()

{

   vector <int> vec1, vec2;

   vector <int>::iterator Iter1;

   int i;

   for(i = 0; i <= 5; i++)

     vec1.push_back(5*i);

   for(i = 0; i <= 2; i++)

     vec1.push_back(5);

   for(i = 0; i <= 5; i++)

     vec1.push_back(5*i);

   for(i = 0; i <= 2; i++)

     vec1.push_back(5);

   cout<<"Vector vec1 data: ";

   for(Iter1 = vec1.begin(); Iter1 != vec1.end(); Iter1++)

      cout<<*Iter1<<" ";

   cout<<endl;

   // searching vec1 for first match to (5 5 5) under identity

   vector <int>::iterator result1;

   result1 = search_n(vec1.begin(), vec1.end(), 3, 5);

   if(result1 == vec1.end())

      cout<<"\nThere is no match for a sequence (5 5 5) in vec1."<<endl;

   else

      cout<<"\nThere is at least one match of a sequence (5 5 5)\nin vec1 and the first one begins at "

          <<"position "<<result1 - vec1.begin()<<endl;

   // searching vec1 for first match to (5 5 5) under twice

   vector <int>::iterator result2;

   result2 = search_n(vec1.begin(), vec1.end(), 3, 5);

   if(result2 == vec1.end())

      cout<<"\nThere is no match for a sequence (5 5 5) in vec1 under the equivalence predicate twice."<<endl;

   else

      cout<<"\nThere is a match of a sequence (5 5 5) under the equivalence\npredicate twice"

          <<" in vec1 and the first one begins at position "<<result1 - vec1.begin()<<endl;

}

[bodo@bakawali ~]$ g++ algosearchn.cpp -o algosearchn

[bodo@bakawali ~]$ ./algosearchn

Vector vec1 data: 0 5 10 15 20 25 5 5 5 0 5 10 15 20 25 5 5 5

There is at least one match of a sequence (5 5 5)

in vec1 and the first one begins at position 6

There is a match of a sequence (5 5 5) under the equivalence

predicate twice in vec1 and the first one begins at position 6

tenouk C++ STL tutorial

Further C++ STL algorithm related reading:

1. Source code for this tutorial is available inC++ STL Algorithm source code.

2. Acomplete C Standard Library.

3. Acomplete C++ Standard Library documentation that includes STL.

4. Check thebest selling C / C++ and STL books at Amazon.com.

5. C++ Templates programming tutorials.

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C++ STL Algorithm Classes:  Part 1 | Part 2 |Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 |Part 9 | Part 10 |Part 11 | Part 12 | Part 13 | Part 14 | Part 15