Data commit

Task/ISBN13-check-digit/Java/isbn13-check-digit-1.java

@@ -0,0 +1,38 @@
+public static void main(String[] args) {
+    String[] isbn13s = {
+        "978-0596528126",
+        "978-0596528120",
+        "978-1788399081",
+        "978-1788399083"
+    };
+    for (String isbn13 : isbn13s)
+        System.out.printf("%s %b%n", isbn13, validateISBN13(isbn13));
+}
+
+static boolean validateISBN13(String string) {
+    int[] digits = digits(string.strip().replace("-", ""));
+    return digits[12] == checksum(digits);
+}
+
+static int[] digits(String string) {
+    int[] digits = new int[13];
+    int index = 0;
+    for (char character : string.toCharArray()) {
+        if (character < '0' || character > '9')
+            throw new IllegalArgumentException("Invalid ISBN-13");
+        /* convert ascii to integer */
+        digits[index++] = Character.digit(character, 10);
+    }
+    return digits;
+}
+
+static int checksum(int[] digits) {
+    int total = 0;
+    int index = 0;
+    for (int digit : digits) {
+        if (index == 12) break;
+        if (index++ % 2 == 1) digit *= 3;
+        total += digit;
+    }
+    return 10 - (total % 10);
+}

Task/ISBN13-check-digit/Java/isbn13-check-digit-2.java

@@ -0,0 +1,18 @@
+public static void main(){
+        System.out.println(isISBN13("978-1734314502"));
+        System.out.println(isISBN13("978-1734314509"));
+        System.out.println(isISBN13("978-1788399081"));
+        System.out.println(isISBN13("978-1788399083"));
+    }
+public static boolean isISBN13(String in){
+        int pre = Integer.parseInt(in.substring(0,3));
+        if (pre!=978)return false;
+        String postStr = in.substring(4);
+        if (postStr.length()!=10)return false;
+        int post = Integer.parseInt(postStr);
+        int sum = 38;
+        for(int x = 0; x<10;x+=2)
+        sum += (postStr.charAt(x)-48)*3 + ((postStr.charAt(x+1)-48));
+        if(sum%10==0) return true;
+        return false;
+    }