Starting Recursion

[just another thug]

We are currently starting recursion in my Computer Science class and while the concept isn't that tought to grasp, the code can be. We have already played with 'The Towers of Hanoi' and I have it down pat. Now we must display Pascal's Triangle recursively, and I am having trouble with some of the coding. I keep throwing IndexOutOfBounds with my arrays. Basically, I have a two dimensional array holding the triangle value. I'm sorry I do not have the exact code of the main method where it occurs, I'll get that to you all once I get to school. Basically, maybe some pseudocode would be nice to see if I am following the same idea that you all are.

[CrazyDude]

I'm pretty good with java, but I have zero clue what you just said.

[just another thug]

 

I'm pretty good with java, but I have zero clue what you just said.

Okay to sum up the problem we must display Pascals triangle recusively.

 

........1

......1 1

....1 2 1

...1 3 3 1

.1 4 6 4 1

 

Pascal's trianlge is where the number on the bottom row is the sum of the two numbers directly above it.

[Svip]

Perhaps this page will explain a lot:

 

http://en.wikipedia.org/wiki/Pascals_triangle

 

And even perhaps it may explain how to write your application, which I have yet to understand the need of.

[Jevon]

It's kinda difficult to advise you without seeing what you have already. Below is some code I knocked up in about 5-10 minutes in C# - it won't translate directly, but it's a different approach to using two-dimensional arrays. Recursion generally means you don't need historic data anyway, which is the only reason I can think of for a two-dimension array in this case.

 

using System;namespace Pascal_Triangle {   class Program {       static void Main( string[] args ) {           int[] oldRow = { 1 };           int[] newRow = null;           for ( int counter = 0; counter < 15; counter++ ) {               string output = string.Empty;               foreach ( int curVal in oldRow ) {                   output += curVal + ",";               }               output = output.Substring( 0, output.Length - 1 );               Console.WriteLine( output );               newRow = new int[ oldRow.Length + 1 ];               int lastValue = 0;               newRow[ newRow.Length - 1 ] = 1;               for ( int rowIndex = 0; rowIndex < newRow.Length - 1; rowIndex++ ) {                   newRow[ rowIndex ] = lastValue + oldRow[ rowIndex ];                   lastValue = oldRow[ rowIndex ];               }               oldRow = newRow;           }           Console.ReadKey();       }   }}