class R16_R22 {

// R1.6 revisited -- see also 4/10 lecture sketch

    // upper-case dna strand complementary to $in$.  case is ignored.
    // example: $System.out.println(complement("taCaGCgATAcgtg"));$
    public static String complement(String in) {
        in = in.toUpperCase(); // added [4/11]
        String out = "";
        int i = 0;
        while (i < in.length()) {
            char c = in.charAt(i);
            if (c == 'A') {
                out = out + 'T'; // or: out = out + "T";
            } else if (c == 'T') {
                out = out + 'A'; // or: out = out + "A";
            } else if (c == 'G') {
                out = out + 'C'; // or: out = out + "C";
            } else {
                out = out + 'G'; // or: out = out + "G";
            }
            i = i + 1;
        }
        return out;
        // NOTE: $out +=$ can be used instead of $out = out +$.
    }
    /* matlab equivalent:
    
    function out = complement(in)
    % out = complement(in): return uppercase dna strand complementary to $in$.
    % case is ignored.  example: $complement('taCaGCgATAcgtg')$
        out = '';
        i = 1;
        while i <= length(in)
            c = in[i];
            if c == 'A'
                out = [out 'T'];
            elseif c == 'T'
                out = [out 'A'];
            elseif c == 'G'
                out = [out 'C'];
            else
                out = [out 'G'];
            end
            i = i+1;
        end
    */

// R2.2 revisited

    // "$isbn$ is a valid ISBN string?".  ignore case.
    public static boolean checkisbn(String isbn) {
        if (isbn.length() != 10) {
            return false;
        }
    
        int want = -1; // desired value of checksum
        if (isbn.charAt(9) == 'X' || isbn.charAt(9) == 'x') {
            want = 10; 
        } else if ('0' <= isbn.charAt(9) & isbn.charAt(9) <= '9') {
            want = isbn.charAt(9) - '0';
        } else { //  last character is not a digit, $'x'$, or $'X'$ -- bad!
            return false;
        }
    
        int i = 0;
        int star = 0;
        // inv: star = sum of first $i$ out of all 9 terms of checksum
        while (i != 9) {
            if ('0' <= isbn.charAt(i) & isbn.charAt(i) <= '9') {
                star += (isbn.charAt(i) - '0') * (i+1);
            } else { // not a digit -- bad!
                return false;
            }
            i = i+1;
        }
        return star % 11 == want;
    }
    
    /* matlab equivalent:
    
    function ok = checkisbn(isbn)
    % ok = checkisbn(isbn): return "$isbn$ is a valid ISBN string?". ignore case.
    
        if length(isbn) ~= 10
            ok = logical(0);
            return
        end
    
        if isbn(10) == 'X' | isbn(10) == 'x'
            want = 10; % desired value of checksum
        elseif ('0' <= isbn(10) & isbn(10) <= '9')
            want = isbn(10) - '0'; % desired value of checksum
        else % last character is not a digit, $'x'$, or $'X'$ -- bad!
            ok = logical(0);
            return
        end
    
        i = 0; star = 0;
        % inv: star = sum of first $i$ out of all 9 terms of checksum
        while i ~= 9
            i = i+1;
            if ('0' <= isbn(i) & isbn(i) <= '9')
                star = star + (isbn(i) - '0') * i;
            else % not a digit -- bad!
                ok = logical(0);
                return;
            end
        end
        ok = rem(star, 11) == want;
    */

// sample calls to $complement$ and $checkisbn$

    // run $complement$ and $checkisbn$ on some sample test cases
    public static void main(String[] args) {
    String[] dna = new String[] {
        "taCaGCgATAcgtg",
        "aTGTcgcTATGcAC",
        "",
        "a",
        "G",
        "AtTaCatGagTagTatAct" };
    int i = 0;
    while (i < dna.length) {
        System.out.println("complement of `" + dna[i] + "' is `" + 
        complement(dna[i]) + "'");
        i += 1;
    }

    String[] isbn = new String[] {
            "0812544501",
            "156389016X",
            "812544501",
            "0712544501" };
    i = 0;
    while (i < isbn.length) {
        System.out.println("`" + isbn[i] + "' is valid ISBN number: " + 
        checkisbn(isbn[i]));
        i += 1;
    }
    }

}