Strings.java

package modern.challenge;

import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
import java.util.stream.Collectors;

public final class Strings {

    private Strings() {
        throw new AssertionError("Cannot be instantiated");
    }

    public static String removeDuplicatesV1(String str) {

        if (str == null || str.isEmpty()) {
            // or throw IllegalArgumentException
            return "";
        }

        char[] chArray = str.toCharArray();
        StringBuilder sb = new StringBuilder();
        for (char ch : chArray) {
            if (sb.indexOf(String.valueOf(ch)) == -1) {
                sb.append(ch);
            }
        }

        return sb.toString();
    }

    public static String removeDuplicatesV2(String str) {

        if (str == null || str.isEmpty()) {
            // or throw IllegalArgumentException
            return "";
        }

        char[] chArray = str.toCharArray();
        StringBuilder sb = new StringBuilder();
        Set<Character> chHashSet = new HashSet<>();
        for (char c : chArray) {
            if (chHashSet.add(c)) {
                sb.append(c);
            }

        }
        return sb.toString();
    }

    public static String removeDuplicatesV3(String str) {

        if (str == null || str.isEmpty()) {
            // or throw IllegalArgumentException
            return "";
        }

        return Arrays.asList(str.split("")).stream()
                .distinct()
                .collect(Collectors.joining());
    }
}