Cesarion Cesarion - 1 month ago 7
Java Question

Recursive to Iterative Pascal's Triangle

I wonder how to convert a recursive function/class to an iterative one.
I have made a recursive Pascal's triangle, and now need to compare it to an iterative.

public class RecursivePascal extends ErrorPascal implements Pascal
{
private int n;

RecursivePascal(int n) throws Exception
{
super(n);
this.n = n;
}

public void printPascal()
{
printPascal(n, false);
}

public void printPascal(boolean upsideDown)
{
printPascal(n, upsideDown);
}

private void printPascal(int n, boolean upsideDown)
{
if (n == 0) { return; }

if (!upsideDown) { printPascal(n - 1, upsideDown); }

for (int i = 0; i < n; i++)
{
System.out.print(binom(n - 1, i) + (n == i + 1 ? "\n" : " "));
}

if (upsideDown) { printPascal(n - 1, upsideDown); }
}

public int binom(int n, int k)
{
if (k == 0 || n == k) { return 1; }

return binom(n - 1, k - 1) + binom(n - 1, k);
}
}


What do I need to change in order to make it iterative? I'm still a little unsure of how this works. Thanks in advance!

Answer

Plug these two functions below into a pascal class. I tested it and it works. That link that Prateek Darmwal posted is pretty much the same thing.

  public void nonRecursivePrint()
  {
    nonRecursivePrint(n, true);
  }

  public void nonRecursivePrint(int n, boolean upsideDown)
  {
    if (!upsideDown)
    {
      for (int j=0; j<(n+1); j++)
      {
        for (int i=0; i<(j); i++)
        {
          System.out.print(binom(j - 1, i) + (j == i + 1 ? "\n" : " "));
        }
      }
    }
    else
    {
      for (int j=n; j>0; j--)
      {
        for (int i=0; i<(j); i++)
        {
        System.out.print(binom(j - 1, i) + (j == i + 1 ? "\n" : " "));
        }
      }
    }       
  }