import java.util.Arrays;

public class Base64 {

    public static void main(String[] args) {
        byte[] bytes = "ABCDEFG".getBytes();
        String encoded = encode(bytes);
        if (encoded.equals("QUJDREVGRw==") == false) {
            throw new AssertionError(encoded);
        }

        byte[] decoded = decode(encoded);
        if (Arrays.equals(decoded, bytes) == false) {
            throw new AssertionError(new String(decoded));
        }
    }

    private static final char[] CONVERSION_TABLE =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
            .toCharArray();

    public static String encode(byte[] bs) {
        int l = bs.length;
        int q = l / 3;
        int m = l % 3;
        char[] cs = new char[(q + (m == 0 ? 0 : 1)) * 4];
        int index = 0;
        for (int i = 0; i < q; i++) {
            int a = bs[i * 3] << 16 | bs[i * 3 + 1] << 8 | bs[i * 3 + 2];
            cs[index++] = CONVERSION_TABLE[a >> 18 & 0x3f];
            cs[index++] = CONVERSION_TABLE[a >> 12 & 0x3f];
            cs[index++] = CONVERSION_TABLE[a >> 6 & 0x3f];
            cs[index++] = CONVERSION_TABLE[a & 0x3f];
        }
        if (m == 2) {
            int a = bs[l - 2] << 8 | bs[l - 1];
            cs[index++] = CONVERSION_TABLE[a >> 10 & 0x3f];
            cs[index++] = CONVERSION_TABLE[a >> 4 & 0x3f];
            cs[index++] = CONVERSION_TABLE[a << 2 & 0x3f];
        } else if (m == 1) {
            int a = bs[l - 1];
            cs[index++] = CONVERSION_TABLE[a >> 2 & 0x3f];
            cs[index++] = CONVERSION_TABLE[a << 4 & 0x3f];
        }
        while (index < cs.length) {
            cs[index++] = '=';
        }
        return String.valueOf(cs);
    }

    public static byte[] decode(String text) {
        char[] cs = text.toCharArray();
        int q = cs.length / 4;
        byte[] bs = new byte[q * 3];
        int index = 0;
        for (int i = 0; i < q; i++) {
            int a =
                indexOf(cs[i * 4]) << 18
                    | indexOf(cs[i * 4 + 1]) << 12
                    | indexOf(cs[i * 4 + 2]) << 6
                    | indexOf(cs[i * 4 + 3]);
            bs[index++] = (byte) (a >> 16);
            bs[index++] = (byte) (a >> 8);
            bs[index++] = (byte) a;
        }
        while (bs[--index] == 0) {
        }
        return Arrays.copyOf(bs, index + 1);
    }

    private static int indexOf(char c) {
        if (c == '+') {
            return 62;
        } else if (c == '/') {
            return 63;
        } else if ('A' <= c && c <= 'Z') {
            return c - 65;
        } else if ('a' <= c && c <= 'z') {
            return c - 71;
        } else if ('0' <= c && c <= '9') {
            return c + 4;
        }
        return 0;
    }
}