Print a pattern without using any loop - GeeksforGeeks

Print a pattern without using any loop - GeeksforGeeks
Given a number n, print following pattern without using any loop.

Input: n = 16
Output: 16, 11, 6, 1, -4, 1, 6, 11, 16

Input: n = 10
Output: 10, 5, 0, 5, 10

We basically first reduce 5 one by one until we reach a negative or 0. After we reach 0 or negative, we one one add 5 until we reach n.

The code uses a flag variable to indicate whether we are moving toward 0 or we are moving toward back to n.

// Recursive function to print the pattern.

// n indicates input value

// m indicates current value to be printed

// flag indicates whether we need to add 5 or

// subtract 5.  Initially flag is true.

void printPattern(int n, int m, bool flag)

{

    // Print m.

    cout << m << " ";

    

    // If we are moving back toward the n and

    // we have reached there, then we are done

    if (flag == false && n ==m)

        return; 

    

    // If we are moving toward 0 or negative.

    if (flag)

    {

      // If m is greater, then 5, recur with true flag

      if (m-5 > 0)

         printPattern(n, m-5, true);

      else // recur with false flag

         printPattern(n, m-5, false);

    }

    else // If flag is false.

         printPattern(n, m+5, false);

}

 We can use two print statements. First one before recursive call that prints all decreasing sequence. Second one after the recursive call to print increasing sequence.

// Recursive function to print the pattern without any extra

// variable

void printPattern(int n)

{

     // Base case (When n becomes 0 or negative) 

     if (n ==0 || n<0)

     {

        cout << n << " ";

        return; 

     }

    

     // First print decreasing order

     cout << n << " ";

     printPattern(n-5);

 

     // Then print increasing order

     cout << n << " ";  

}

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