Initial data commit

Task/SHA-256-Merkle-tree/Java/sha-256-merkle-tree.java

@@ -0,0 +1,58 @@
+import java.io.*;
+import java.security.*;
+import java.util.*;
+
+public class SHA256MerkleTree {
+    public static void main(String[] args) {
+        if (args.length != 1) {
+            System.err.println("missing file argument");
+            System.exit(1);
+        }
+        try (InputStream in = new BufferedInputStream(new FileInputStream(args[0]))) {
+            byte[] digest = sha256MerkleTree(in, 1024);
+            if (digest != null)
+                System.out.println(digestToString(digest));
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+
+    private static String digestToString(byte[] digest) {
+        StringBuilder result = new StringBuilder();
+        for (int i = 0; i < digest.length; ++i)
+            result.append(String.format("%02x", digest[i]));
+        return result.toString();
+    }
+
+    private static byte[] sha256MerkleTree(InputStream in, int blockSize) throws Exception {
+        byte[] buffer = new byte[blockSize];
+        int bytes;
+        MessageDigest md = MessageDigest.getInstance("SHA-256");
+        List<byte[]> digests = new ArrayList<>();
+        while ((bytes = in.read(buffer)) > 0) {
+            md.reset();
+            md.update(buffer, 0, bytes);
+            digests.add(md.digest());
+        }
+        int length = digests.size();
+        if (length == 0)
+            return null;
+        while (length > 1) {
+            int j = 0;
+            for (int i = 0; i < length; i += 2, ++j) {
+                byte[] digest1 = digests.get(i);
+                if (i + 1 < length) {
+                    byte[] digest2 = digests.get(i + 1);
+                    md.reset();
+                    md.update(digest1);
+                    md.update(digest2);
+                    digests.set(j, md.digest());
+                } else {
+                    digests.set(j, digest1);
+                }
+            }
+            length = j;
+        }
+        return digests.get(0);
+    }
+}