(solved)C++ program to print all the contiguous (continuous) subsequences of an array

Explanation and Notes

Suppose we have been given an array of certain number of elements. And we have to print subsequences from a starting index to an ending index.

We will use two variables for the two markers: the first will be for the start of a subsequence, and the second for the end.

In the programs below, the variable i has been used as the first or starting marker, and the variable j as the ending marker.

The variable i increments from 0 to end of the array.

To understand the operation consider that i is currently placed at, say, index 2. The variable j will start incrementing from index 2. So we will have the values of i and j like so: (i = 2, j = 2), (i = 2, j = 3), (i = 2, j = 4), and so on. Thus, i and j represent the bounds of various subsequences starting at index 2.

A for-loop of k prints the array between i and j!

Please watch the video solution given below for more detail.

Method 1
(using vectors in C++)

Following program uses a vector to hold the elements of the array. If you are not conversant with vectors, then refer to Method 2 next.

// program to print all subsequences 
// of an array 
#include <iostream>

#include <vector>

using namespace std;

int main()
{

  std::vector<int> vec = { 4, 0, -7 };

  // start marker 
  for (unsigned i = 0; i < vec.size(); i++)
  {

    // end marker 
    for (unsigned j = i; j < vec.size(); j++)
    {

      // print from start to end inclusive 
      for (unsigned k = i; k <= j; k++)
      {

        cout << vec[k] << "; ";

      }

      cout << endl;

    }

  }

  return 0;

}

Method 2
(using arrays in C++)

This program is exactly same as the one given in method 1 above, except that it uses a char array.

// program to print all subsequences 
// of an array 
#include <iostream>

using namespace std;

int main()
{

  int arr[] = { 5, -1, 0, 8, 7, -2 };

  // number of elements in the array 
  const int SIZE = sizeof(arr) / sizeof(*arr);

  // start marker 
  for (int i = 0; i < SIZE; i++)
  {

    // end marker 
    for (int j = i; j < SIZE; j++)
    {

      // print the array from i to j 
      for (int k = i; k <= j; k++)
      {

        cout << arr[k] << "; ";

      }

      cout << endl;

    }

  }

  return 0;

}

Comments and Discussion

Leave your comments on the youtube comments box.

Method 3
(not recommended, but works)

This method is neither more efficient, nor systematic. But I have included here because this was written during one of my attempts. I didn't want to throw it away.

// program to print all subsequencies 
// of an array 
#include <iostream>

using namespace std;

int main()
{

  int arr[] = { 5, -1, 0, 8, 7, -2 };

  // number of elements in the array 
  const int SIZE = sizeof(arr) / sizeof(*arr);

  for (int i = 0; i < SIZE; i++)
  {

    for (int j = 1; j <= (SIZE - i); j++)
    {

      for (int k = 0; k < j; k++)
      {

        cout << arr[i + k] << "; ";

      }

      cout << endl;

    }

  }

  return 0;

}