merkle tree for verification of large datasets

Author: Arjiit

Design/MerkleTree.java

@@ -0,0 +1,92 @@
+public class MerkleTree {
+
+	/*
+		Merkle trees allow for effecient and secure verification of large data structures. 
+		With the structure of tree, we can easily identify map large amounts of data and
+		easily identify where changes in the data occur.
+	*/
+
+	private static class Node {
+		String data;
+		Node left;
+		Node right;
+		Node(String value) {
+			this.data = value;
+		}
+
+	}
+
+	private Node root;
+
+	public static void main(String[] args) {
+		Queue<Node> q = new LinkedList<>();
+		q.add(new Node("A"));
+		q.add(new Node("B"));
+		q.add(new Node("C"));
+		q.add(new Node("D"));
+		q.add(new Node("E"));
+		MerkleTree mt = new MerkleTree();
+		Node root1 = mt.buildTree(q);
+
+		Queue<Node> q2 = new LinkedList<>();
+		q2.add(new Node("AA")); // data changed here
+		q2.add(new Node("B"));
+		q2.add(new Node("C"));
+		q2.add(new Node("D"));
+		q2.add(new Node("E"));
+		MerkleTree mt2 = new MerkleTree();
+		Node root2 = mt.buildTree(q);
+
+		if (mt.detectChange(root1, root2)) {
+			 root1 = mt.mergeChange(root1, root2);
+		}
+			
+	}
+
+
+	public Node buildTree(Queue<Node> q) {
+		if (q.pop() == null) {
+			return;
+		}
+		Node new_node = q.pop();
+		new_node.left = buildTree(q);
+		new_node.right = buildTree(q);
+
+		CRC32 crc = new CRC32();
+		crc.update((new_node.left.data + (new_node.right != null) ? new_node.right.data : "").getBytes());
+		Node root = new Node(crc.getValue() + "");
+		return root;
+	}
+
+	public boolean detectChange(Node refNode, Node newNode) {
+		if (refNode == null && new_node == null) return false; // no change, base check
+		if (refNode == null || new_node == null) return true; // change detected, data added/deleted
+
+		boolean leftChanged = detectChange(refNode.left, new_node.left);
+		boolean rightChanged = detectChange(refNode.right, new_node.right);
+		if (refNode.data != new_node.data) return true;
+
+		return leftChanged || rightChanged;
+	}
+
+
+	public Node mergeChange(Node refNode, Node new_node) {
+		if (refNode == null && new_node == null) return null;
+		else if (refNode != null && new_node == null) {
+			return null; //changed detected. Data deleted
+		}
+
+		else if (refNode == null && new_node != null) {
+			return new_node; // change deteced. Data added
+		}
+		else if (refNode.data != new_node.data) {
+			refNode.data = new_node.data;
+		}
+		refNode.left = mergeChange(refNode.left, new_node.left);
+		refNode.right = mergeChange(refNode.right, new_node.right);
+
+		return refNode;
+	}
+
+
+}