Serialize and Deserialize a Binary Tree (pre order).

SerializingBinaryTree.java

class TreeNode{
    int val;
    TreeNode left, right;
    TreeNode(int val){
        this.val = val;
    }
}

public String serialize(TreeNode root){
    StringBuilder sb = new StringBuilder();
    serialize(root, sb);
    return sb.toString();
}

private void serialize(TreeNode x, StringBuilder sb){
    if (x == null) {
        sb.append("# ");
    } else {
        sb.append(x.val + " ");
        serialzie(x.left, sb);
        serialzie(x.right, sb);
    }
}

public TreeNode deserialize(String s){
    if (s == null || s.length() == 0) return null;
    StringTokenizer st = new StringTokenizer(s, " ");
    return deserialize(st);
}

private TreeNode deserialize(StringTokenizer st){
    if (!st.hasMoreTokens())
        return null;
    String val = st.nextToken();
    if (val.equals("#"))
        return null;
    TreeNode root = new TreeNode(Integer.parseInt(val));
    root.left = deserialize(st);
    root.right = deserialize(st);
    return root;
}