In Keynote, break the visualization up into multiple slides and use the 'Magic Move' slide transition to handle figuring out most of the moves for you. You don't need to go as large as text, but limit the number of lines of code to 12 to 15 on a slide. Often when showing code in a presentation, you will want to show code snippets that change between slides as a result of demonstrating new APIs or just as a different example.