strings_HasAllUniqueCharacters.java

package com.danielvaughan.ctci.strings;

/**
 * Created with IntelliJ IDEA.
 * User: dvaughan
 * Date: 13/07/2013
 * Time: 13:48
 * To change this template use File | Settings | File Templates.
 */
public class HasAllUniqueCharacters {

    public boolean hasAllUniqueCharacters(final String string)
    {
        if (string==null || string.length()==0)
        {
            return false;
        }
        if (string.length()==1)
        {
            return true;
        }
        String first = string.substring(0,1);
        String rest = string.substring(1);
        if (rest.contains(first))
        {
            return false;
        }
        else
        {
            return hasAllUniqueCharacters(rest);
        }
    }

    public static void main(String [] args)
    {
        HasAllUniqueCharacters hauc = new HasAllUniqueCharacters();
        String uniqueString = "abcdefgh";
        String nonUniqueString = "abcdefab";
        System.out.println(uniqueString + " " + hauc.hasAllUniqueCharacters(uniqueString));
        System.out.println(nonUniqueString + " " + hauc.hasAllUniqueCharacters(nonUniqueString));
    }
}

strings_Permutation.java

package com.danielvaughan.ctci.strings;

import java.util.HashMap;
import java.util.Map;

/**
 * Created with IntelliJ IDEA.
 * User: dvaughan
 * Date: 13/07/2013
 * Time: 14:00
 * To change this template use File | Settings | File Templates.
 */
public class Permutation {

    public boolean isPermutation (final String stringA, final String stringB)
    {
        if (stringA.length() != stringB.length())
        {
            return false;
        }
        Map<Character, Integer> aCharCount = new HashMap<Character, Integer>();
        Map<Character, Integer> bCharCount = new HashMap<Character, Integer>();
        for (int i=0; i<stringA.length(); i++)
        {
            char aChar = stringA.charAt(i);
            char bChar = stringB.charAt(i);
            int currentACount = aCharCount.get(aChar)==null ? 0 : aCharCount.get(aChar);
            int currentBCount = bCharCount.get(bChar)==null ? 0 : bCharCount.get(bChar);
            aCharCount.put(aChar, currentACount++);
            bCharCount.put(bChar, currentBCount++);
        }
        for (Character key : aCharCount.keySet())
        {
            if (aCharCount.get(key) != bCharCount.get(key))
            {
                return false;
            }
        }
        return true;
    }

    public static void main(String [] args)
    {
        Permutation permutation = new Permutation();
        String string = "abcdefgh";
        String permString = "hgfedcba" ;
        String nonPermString = "abcdefab";
        System.out.println(permString + " " + permutation.isPermutation(string, permString));
        System.out.println(nonPermString + " " + permutation.isPermutation(string, nonPermString));
    }
}