Initial data commit

Task/Long-multiplication/Java/long-multiplication-1.java

@@ -0,0 +1,51 @@
+public class LongMult {
+
+	private static byte[] stringToDigits(String num) {
+		byte[] result = new byte[num.length()];
+		for (int i = 0; i < num.length(); i++) {
+			char c = num.charAt(i);
+			if (c < '0' || c > '9') {
+				throw new IllegalArgumentException("Invalid digit " + c
+						+ " found at position " + i);
+			}
+			result[num.length() - 1 - i] = (byte) (c - '0');
+		}
+		return result;
+	}
+
+	public static String longMult(String num1, String num2) {
+		byte[] left = stringToDigits(num1);
+		byte[] right = stringToDigits(num2);
+		byte[] result = new byte[left.length + right.length];
+		for (int rightPos = 0; rightPos < right.length; rightPos++) {
+			byte rightDigit = right[rightPos];
+			byte temp = 0;
+			for (int leftPos = 0; leftPos < left.length; leftPos++) {
+				temp += result[leftPos + rightPos];
+				temp += rightDigit * left[leftPos];
+				result[leftPos + rightPos] = (byte) (temp % 10);
+				temp /= 10;
+			}
+			int destPos = rightPos + left.length;
+			while (temp != 0) {
+				temp += result[destPos] & 0xFFFFFFFFL;
+				result[destPos] = (byte) (temp % 10);
+				temp /= 10;
+				destPos++;
+			}
+		}
+		StringBuilder stringResultBuilder = new StringBuilder(result.length);
+		for (int i = result.length - 1; i >= 0; i--) {
+			byte digit = result[i];
+			if (digit != 0 || stringResultBuilder.length() > 0) {
+				stringResultBuilder.append((char) (digit + '0'));
+			}
+		}
+		return stringResultBuilder.toString();
+	}
+
+	public static void main(String[] args) {
+		System.out.println(longMult("18446744073709551616",
+				"18446744073709551616"));
+	}
+}