init impl

for BST, preorder is enough to serialize and deserialize it.

Author: freemanzhang

src/binarySearchTree/SerializeDeserializeBST.java

@@ -0,0 +1,72 @@
+package binarySearchTree;
+
+import utility.TreeNode;
+
+/*
+Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, 
+or transmitted across a network connection link to be reconstructed later in the same or another computer environment.
+
+Design an algorithm to serialize and deserialize a binary search tree. There is no restriction on how your serialization/deserialization algorithm should work. 
+You just need to ensure that a binary search tree can be serialized to a string and this string can be deserialized to the original tree structure.
+
+The encoded string should be as compact as possible.
+
+Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.
+ * */
+
+public class SerializeDeserializeBST
+{
+    // Encodes a tree to a single string.
+	public String serialize( TreeNode root )
+	{ 
+		// preorder
+		StringBuilder sb = new StringBuilder();
+		serializedfs( root, sb );
+		return sb.toString();
+	}
+
+	private void serializedfs( TreeNode root, StringBuilder sb )
+	{
+		if ( root == null )
+			return; // no "null "
+		sb.append( root.val ).append( " " );
+		serializedfs( root.left, sb );
+		serializedfs( root.right, sb );
+	}
+
+	public TreeNode deserialize( String data )
+	{
+		if ( data.length() == 0 )
+			return null;
+		String[] list = data.split( " " );
+		TreeNode dummy = new TreeNode( 0 );
+		deserializedfs( list, 0, dummy, true, Integer.MIN_VALUE, Integer.MAX_VALUE );
+		return dummy.left;
+	}
+
+	private int deserializedfs( String[] list, int pos, TreeNode root, boolean isleft, int lower, int upper )
+	{
+		if ( pos >= list.length )
+			return pos;
+
+		int val = Integer.valueOf( list[pos] );
+		if ( val < lower || val > upper )
+		{
+			return pos - 1; // have not used this pos, so minus one
+		}
+		TreeNode currNode = new TreeNode( val );
+
+		if ( isleft )
+		{
+			root.left = currNode;
+		}
+		else
+		{
+			root.right = currNode;
+		}
+		
+		pos = deserializedfs( list, ++pos, currNode, true, lower, val );
+		pos = deserializedfs( list, ++pos, currNode, false, val, upper );
+		return pos;
+	}
+}