Project Euler - Problem 92

euler.java

package euler;

public class ChainMember {
	private int n;
	
	// we use a -1 as n to indicate that this is a 89 to differ them from 0 or 1
	private static final ChainMember EIGHTYNINE = new ChainMember(-1);
	
	public ChainMember(int n) {
		this.n = n;
	}
	
	private static int next(int n) {
		String s = String.valueOf(n);
		int sum = 0;
		for (int i = 0; i < s.length(); i++) {
			int d = s.charAt(i) - 48;
			sum += d*d;
		}
		return sum;
	}
	
	public ChainMember next() {
		
		if (n == 0) return null;
		if (n == 1) return null;
		if (n == 89) return EIGHTYNINE;
		ChainMember next = new ChainMember(next(n));
		return next;
	}
	
	public boolean is89() {
		return n == -1;
	}
	
	@Override
	public boolean equals(Object obj) {
		if (!(obj instanceof ChainMember)) return false;
		return (n == ((ChainMember) obj).n);
	}
	
	public static void main(String[] args) {
		
		long s = System.currentTimeMillis();
		
		int eightyniners = 0;
		for (int i = 0; i < 10_000_000; i++) {
			ChainMember cm = new ChainMember(i);
			while (cm != null) {
				if (cm.is89()) {
					eightyniners++;
					break;
				}
				cm = cm.next();
			}
		}
		System.out.println(eightyniners);
		System.out.println((System.currentTimeMillis() - s) / 1000 + "s");
	}
	@Override
	public String toString() {
		return String.valueOf(n);
	}
}