Visualizer

import java.util.Arrays;

public class Beaver {

    private Integer[] tape;
    private String[] rules;
    private int index;
    private int rule;


    public Beaver(int len, String[] rules) {
        tape = new Integer[len * 2];
        for (int i = 0; i < len * 2; i++) tape[i] = 0;
        this.rules = rules;
        index = len;
        rule = 0;
        p(rules[0]);
    }

    private boolean eval() {
        String current = rules[rule + (rules.length / 2) * tape[index]];
        if (current.equals("H"))
            return false;
        tape[index] = (int) current.charAt(0) - 48;
        index += current.charAt(1) == 'R' ? 1 : -1;
        rule = current.charAt(2) - 65;
        p(current);
        return !(index == -1 || index == tape.length * 2);
    }

    private void p(String current) {
        String ret = "";
        int ind = 0;
        for (int i : tape) {
            if (ind == index)
                ret += "\u001B[33m";
            else if (i == 0)
                ret += "\u001B[31m";
            else
                ret += "\u001B[32m";

            ret += i + "\u001B[0m";
            ind++;
        }
        ret += " ";
        ret += current;
        System.out.println(ret);
    }


    public void run() {
        int count = 0;
        while (index < tape.length) {
            count++;
            if (!eval())
                break;
        }
        p("");
        System.out.println(count + " Iterations");
    }

    // Put a length and ruleset where it says, uncomment the line, and run
    // 
     public static void main(String[] args) {
     //   Beaver t = new Beaver(INTEGER LENGTH, new String[] {RULES});
        t.run();
     }
}

// Example Rules: Shamelessly stolen from wikipedia https://en.wikipedia.org/wiki/Busy_beaver#Visualizations
// 2 rules  -- 3 wide {"1RB", "1LA", "1LB", "H"}
// 3 rules  -- 5 wide {"1RB", "0RC", "1LC", "H", "1RB", "1LA"}
// 4 Rules  -- 12 wide {"1RB", "1LA", "H", "1RD", "1LB", "0LC", "1LD", "0RA"}
// Skelet 1 (2542/∞ iterations) -- 81 wide {"1LC", "H", "1RD", "1LA", "0LB", "1LE", "1LD", "0LD", "1RE", "0RC"}