MissingLetters

Code

import java.util.Arrays;

public class MissingLetters

{

    public String getMissingLetters(String sentence) {

        sentence = sentence.toUpperCase();

        String res = "";

        for (char c = 'A'; c <= 'Z'; c++)

            if (sentence.indexOf(c) == -1)

                res += c;

        return res;

    }

}

References

https://www.topcoder.com/tc?module=Static&d1=match_editorials&d2=tco03_qual_rd_1