import java.util.stream.Collectors;
import java.util.stream.IntStream;
 
public class Main
{
    public static void main(String args[])
    {
        System.out.println(interleaved("abc", "gfr"));
        System.out.println(String.valueOf(interleaved("abc".toCharArray(), "gfr".toCharArray())));
    }
    static String interleaved(String a, String b)
    {
        assert a.length() == b.length();
        return IntStream.range(0, Math.min(a.length(), b.length()))
                .mapToObj(i -> a.substring(i, i+1) + b.substring(i, i+1))
                .collect(Collectors.joining());
    }
    static char[] interleaved(char[] a, char[] b)
    {
        assert a.length == b.length;
        char[] result = new char[a.length + b.length];
        for (int i = 0; i < a.length; ++i) {
            result[2*i] = a[i];     // result[::2] = a
            result[2*i+1] = b[i];   // result[1::2] = b
        }
        return result;
    }
}

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