Add proof solution

Author: jagdish-15

exercises/practice/intergalactic-transmission/.meta/src/reference/java/IntergalacticTransmission.java

@@ -1,13 +1,82 @@
+import java.util.ArrayList;
 import java.util.List;
 
 public class IntergalacticTransmission {
 
-	public static List<String> getTransmitSequence(List<String> message) {
-		throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
-	}
+    private static final byte INIT_UPPER_MASK = (byte) 0xFE;
 
-	public static List<String> decodeSequence(List<String> sequence) {
-		throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
-	}
+    public static List<Integer> getTransmitSequence(List<Integer> message) {
+        List<Integer> transmitSeq = new ArrayList<>();
+        byte carry = 0;
+        byte upperMask = INIT_UPPER_MASK;
 
+        for (int i = 0; i < message.size(); i++) {
+            byte currentByte = message.get(i).byteValue();
+
+            if (upperMask == 0) {
+                transmitSeq.add((int) addParity(carry) & 0xFF);
+                carry = 0;
+                upperMask = (byte) 0xFE;
+            }
+
+            int shiftPlaces = Integer.numberOfTrailingZeros(upperMask & 0xFF);
+            int current = ((carry & 0xFF) << (8 - shiftPlaces)) | ((currentByte & 0xFF) >>> shiftPlaces);
+            transmitSeq.add((int) addParity((byte) current) & 0xFF);
+
+            carry = (byte) (currentByte & ~upperMask);
+            upperMask = (byte) (upperMask << 1);
+        }
+
+        if (upperMask != INIT_UPPER_MASK) {
+            byte lastGroup = (byte) ((carry & 0xFF) << Integer.bitCount(upperMask & 0xFF));
+            transmitSeq.add((int) addParity(lastGroup) & 0xFF);
+        }
+
+        return transmitSeq;
+    }
+
+    private static byte addParity(byte source) {
+        if (Integer.bitCount(source & 0x7F) % 2 == 0) {
+            return (byte) (source << 1);
+        } else {
+            return (byte) ((source << 1) | 1);
+        }
+    }
+
+    public static List<Integer> decodeSequence(List<Integer> receivedSeq) {
+        if (receivedSeq.isEmpty()) {
+            return new ArrayList<>();
+        }
+
+        List<Integer> decodedMessage = new ArrayList<>();
+        byte byteToAdd = 0x00;
+        byte upperMask = (byte) 0xFF;
+
+        for (int i = 0; i < receivedSeq.size(); i++) {
+            byte currentByte = receivedSeq.get(i).byteValue();
+
+            if (upperMask == (byte) 0xFF) {
+                byteToAdd = getByteData(currentByte);
+                upperMask = (byte) 0x80;
+                continue;
+            }
+
+            byte currentByteData = getByteData(currentByte);
+            int shiftPlaces = Integer.numberOfTrailingZeros(upperMask & 0xFF);
+            byte contribution = (byte) ((currentByteData & 0xFF) >>> shiftPlaces);
+            decodedMessage.add((byteToAdd | contribution) & 0xFF);
+
+            byteToAdd = (byte) (((currentByteData & ~(upperMask | 0x01)) & 0xFF) << Integer.bitCount(upperMask & 0xFF));
+            upperMask = (byte) (((upperMask & 0xFF) >>> 1) | 0x80);
+        }
+
+        return decodedMessage;
+    }
+
+    private static byte getByteData(byte data) {
+        if (Integer.bitCount(data & 0xFF) % 2 != 0) {
+            throw new IllegalArgumentException("Byte has incorrect parity");
+        }
+        return (byte) (data & 0xFE);
+    }
 }

exercises/practice/intergalactic-transmission/src/main/java/IntergalacticTransmission.java

@@ -2,11 +2,11 @@
 
 public class IntergalacticTransmission {
 
-    public static List<String> getTransmitSequence(List<String> message) {
+    public static List<Integer> getTransmitSequence(List<Integer> message) {
         throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
     }
 
-    public static List<String> decodeSequence(List<String> sequence) {
+    public static List<Integer> decodeSequence(List<Integer> sequence) {
         throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
     }