Solved in Java

Instructions

Take 2 strings s1 and s2 including only letters from ato z. Return a new sorted string, the longest possible, containing distinct letters - each taken only once - coming from s1 or s2.

Examples:

a = "xyaabbbccccdefww"
b = "xxxxyyyyabklmopq"
longest(a, b) -> "abcdefklmopqwxy"

a = "abcdefghijklmnopqrstuvwxyz"
longest(a, a) -> "abcdefghijklmnopqrstuvwxyz"
Solution
import java.util.Arrays;
import java.util.LinkedHashSet;
import java.util.Set;

public class TwoToOne {
	
	public static String longest (String s1, String s2) {
		StringBuilder str=new StringBuilder();
		str.append(s1).append(s2);
   char[] chars=str.toString().toCharArray();
   Arrays.sort(chars);
   Set<Character> charSet = new LinkedHashSet<Character>();
   
   for (char c : chars) {
	charSet.add(c);
}
		
		return charSet.toString().replace("[", "").replace("]", "").replace(",", "").replaceAll(" ", "");
    }

}