Example of Multisets

Took this one from Java2s and modified it slightly to show a bit more info.

Example as follows:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//Simple example of multiset

#include <iostream>
#include <set>
#include <algorithm>

using namespace std;

int main()
{
 int a[ 10 ] = { 7, 22, 9, 1, 18, 30, 100, 22, 85, 13 };
 int aSize = sizeof(a) / sizeof(int);
 std::multiset< int, std::less< int > > intMultiset(a, a + aSize);

 cout << "Printing out all the values in the multiset : ";
 multiset<int>::iterator it;
 for ( it = intMultiset.begin(); it != intMultiset.end(); ++it)
   cout << "  " << *it;
 cout << endl << endl;

 std::ostream_iterator< int > output( cout, " " );

 cout << "There are currently " << intMultiset.count( 15 )
      << " values of 15 in the multiset\n\n";

 intMultiset.insert( 15 );
 intMultiset.insert( 15 );

 cout << "After two inserts, there are currently " << intMultiset.count( 15 )
      << " values of 15 in the multiset\n\n";

 cout << "Printing out all the values in the multiset : ";
 for ( it = intMultiset.begin(); it != intMultiset.end(); ++it)
   cout << "  " << *it;
 cout << endl << endl;

 return 0;
}

Output as follows:

Example of set_union and set_intersection

Program as follows:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include <iostream>
#include <algorithm>
#include <vector>
#include <set>

using namespace std;
 
int main()
{
  int setOne[] = {5, 10, 15, 20, 25};
  int setTwo[] = {50, 40, 30, 20, 10, 11, 21, 31, 41, 51};
 
  int setOneSize = sizeof(setOne) / sizeof(int);
  int setTwoSize = sizeof(setTwo) / sizeof(int);
 
  //Its necessary to sort if not already sorted
  sort(setTwo, setTwo + setTwoSize);
 
  vector<int> unionSetVector(setOneSize + setTwoSize); 
  set_union(setOne, setOne + setOneSize, setTwo, setTwo + setTwoSize, unionSetVector.begin());
  
  cout<<"\n1. unionSetVector : ";
  copy(unionSetVector.begin(), unionSetVector.end(), ostream_iterator<int>(cout, " "));
  cout<<endl;
 
  vector<int> intersectionSetVector(min(setOneSize, setTwoSize)); 
  set_intersection(setOne, setOne + setOneSize, setTwo, setTwo + setTwoSize, intersectionSetVector.begin());
 
  cout<<"\n1. intersectionSetVector : ";
  copy(intersectionSetVector.begin(), intersectionSetVector.end(), ostream_iterator<int>(cout, " "));
  cout<<endl;
 
  cout<<endl;
  return 0;
}

The output is as follows:

Example of Algorithm Copy

Sometimes its useful to know the 'copy' method in algorithm class. The following is an example:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
 
//OutputIterator copy ( InputIterator first, InputIterator last, OutputIterator result );

#include<iostream>
#include <algorithm>
#include <vector>

using namespace std;
 
int main()
{
  int someInts[] = {10, 20, 20, 40, 50};
  int someMoreInts[] = {100, 200, 300, 400, 500, 600, 700};
 
  vector<int> someVector;
  vector<int>::iterator someIterator;
 
  //Get the total size of all elements
  int totalSize = (sizeof(someInts) + sizeof(someMoreInts)) / sizeof(int);
 
  //Resize someVector to right size
  someVector.resize(someVector.size() + totalSize);
 
  //Get the number of elements of someInts
  int tempSize = sizeof(someInts) / sizeof(int);
 
  vector<int>::iterator finalElementIt = copy(someInts, someInts + tempSize, someVector.begin());
 
  cout<<"\n1. someVector contains :";
  for(someIterator = someVector.begin(); someIterator != someVector.end(); ++someIterator)
    cout<<"  "<<*someIterator;
  cout<<endl;
 
  //Get size of someMoreInts
  tempSize = sizeof(someMoreInts) / sizeof(int);
 
  copy(someMoreInts, someMoreInts + tempSize, finalElementIt);
 
  cout<<"\n2. someVector contains :";
  for(someIterator = someVector.begin(); someIterator != someVector.end(); ++someIterator)
    cout<<"  "<<*someIterator;
  cout<<endl;
 
  return 0;
}

The output is as follows:

Swap two variables without using third and in one line

Couple of weeks back I was interviewing a fresh graduate. Even though they are taught programming, I am not sure if they take it seriously and learn or practice it well. One of the questions I asked was to swap 2 numbers without using a temp variable.

Looking back now, I think it may be a bigger challenge to ask to swap numbers without using a temp variable and in one line. Below are my three different approaches but I would advise you to try it yourself before looking at the answer.

//Program to swap 2 numbers without using 3rd variable and in one line
//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>

using namespace std;

void approach1(int& a, int& b)
{
  cout<<"\nApproach 1"<<endl;
  a^=b^=a^=b;
}

void approach2(int& a, int& b)
{
  cout<<"\nApproach 2"<<endl;
  //b=(a+b)-(a=b); - This should work but doesnt, why?
  a =((a = a + b) - (b = a - b)); 
}

void approach3(int& a, int& b)
{
  cout<<"\nApproach 3"<<endl;
  a = ((a = a * b) / (b = a / b));
}



int main()
{
  int a = 13, b = 29;
  cout<<"\nOriginal"<<endl;
  cout<<"a = "<<a<<", b = "<<b<<endl;

  approach1(a, b);
  cout<<"a = "<<a<<", b = "<<b<<endl;

  a = 13, b = 29;
  approach2(a, b);
  cout<<"a = "<<a<<", b = "<<b<<endl;

  a = 13, b = 29;
  approach3(a, b);
  cout<<"a = "<<a<<", b = "<<b<<endl;

  return 0;
}

The output is as follows:

Agreed that the above would be applicable only for integers.

Example of Permutations in C++

Example of how you can let the Algorithm class generate permutations of String

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>
#include<algorithm>
#include<string>
#include<vector>

using namespace std;

int main()
{
  string someString="ABC";
  vector<string> someVector;

  someVector.push_back(someString);

  string::iterator itBegin = someString.begin();
  string::iterator itEnd = someString.end();

  while(next_permutation(itBegin, itEnd)) //std::next_permutation defined in algorithm
  {
    someVector.push_back(string(itBegin, itEnd));
  }
  copy(someVector.begin(), someVector.end(), ostream_iterator<string>(cout, "\n"));

  return 0;
}

The output is as follows:

Via: Learning C++: Permutations in C++