TopCoder SRM 144(550) リファクタ後

gistfile1.java

public class BinaryCode {

	public String[] decode(String message) {
		return new String[] { assume('0', message), assume('1', message) };
	}
	
	protected String assume(char p0, String message) {
		char[] q = message.toCharArray();
		int len = q.length;
		char[] p = new char[len];

		p[0] = p0;
		int i, pSum;
		for (i = 0; i < len - 1; i++) {
			pSum = (0 < i ? num(p[i-1]) : 0) + num(p[i]);
			p[i+1] = (char)('0' + num(q[i]) - pSum);
			if ('2' <= p[i+1]) return "NONE";
		}
		pSum = (0 < i ? num(p[i-1]) : 0) + num(p[i]);
		return (num(q[i]) == pSum) ? new String(p) : "NONE";
	}
	
	protected int num(char c) { return c - '0'; }

}