CODEWITHSUNDEEP
javastringhashcode
Saran
Saran

Reputation: 443

Convert hashcode to limited set of string

I know it's one-way function but I want to convert hashcode back to limited set of string (using char between 32 to 126). Is there an efficient way to do this?

Upvotes: 2

Views: 4445

Answers (2)

Peter Lawrey
Peter Lawrey

Reputation: 533790

Actually, I only need one string from that hashcode. I want to make Minecraft seed shortener.

The simplest way to turn an int value into a short string is to use

String s = Integer.toString(n, 36); // uses base 36.

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1503140

It's not only feasible - it's actually pretty simple, given the definition for String.hashCode. You can just create a string of "base 31" characters with some arbitrary starting point to keep everything in the right range, subtracting an offset based on that starting point.

This isn't necessarily the shortest string with the given hash code, but 7 characters is pretty short :)

public class Test {

    public static void main(String[] args) {
        int hash = 100000;
        String sample = getStringForHashCode(hash);
        System.out.println(sample); // ASD^TYQ
        System.out.println(sample.hashCode()); // 100000
    }

    private static final int OFFSET = "AAAAAAA".hashCode();

    private static String getStringForHashCode(int hash) {
        hash -= OFFSET;
        // Treat it as an unsigned long, for simplicity.
        // This avoids having to worry about negative numbers anywhere.
        long longHash = (long) hash & 0xFFFFFFFFL;
        System.out.println(longHash);

        char[] c = new char[7];
        for (int i = 0; i < 7; i++)
        {
            c[6 - i] = (char) ('A' + (longHash % 31));
            longHash /= 31;
        }
        return new String(c);
    }
}

Upvotes: 4

Related Questions