Find string hash collisions in Java.

StringHash.java

import java.util.*;

/**
 * Find String hash collisions.
 * @author Jesper Öqvist <[email protected]>
 */
public class StringHash {
	private static final int NCHAR = 3;
	private static final char[] chars = {
		'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
		'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
		'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
		'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N',
		'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
	};
	private static final int ALPHAS = chars.length;
	public static void main(String[] args) {
		Map<Integer,Collection<String>> map = new HashMap<>();
		int[] index = new int[NCHAR];
		char[] buf = new char[NCHAR];
		while (true) {
			for (int i = 0; i < NCHAR; ++i) {
				buf[i] = chars[index[i]];
			}
			String str = new String(buf);
			int hash = str.hashCode();
			Collection<String> strings = map.get(hash);
			if (strings == null) {
				strings = new LinkedList<String>();
				strings.add(str);
				map.put(hash, strings);
			} else {
				strings.add(str);
			}
			int carry = 1;
			for (int i = 0; i < NCHAR; ++i) {
				index[i] = index[i] + carry;
				carry = index[i] / ALPHAS;
				index[i] %= ALPHAS;
			}
			if (carry > 0) break;
		}

		for (Map.Entry<Integer,Collection<String>> group : map.entrySet()) {
			Collection<String> strings = group.getValue();
			if (strings.size() >= 9) {
				System.out.println("" + group.getKey() + ":");
				for (String str: strings) {
					System.out.println("\t" + str);
				}
			}
		}
	}
}