SplayBST.java


Below is the syntax highlighted version of SplayBST.java from §3.3 Balanced Search Trees.


/******************************************************************************
 *  Compilation:  javac SplayBST.java
 *  Execution:    java SplayBST
 *  Dependencies: none
 *  
 *  Splay tree. Supports splay-insert, -search, and -delete.
 *  Splays on every operation, regardless of the presence of the associated
 *  key prior to that operation.
 *
 *  Written by Josh Israel.
 *
 ******************************************************************************/


public class SplayBST<Key extends Comparable<Key>, Value>  {

    private Node root;   // root of the BST

    // BST helper node data type
    private class Node {
        private Key key;            // key
        private Value value;        // associated data
        private Node left, right;   // left and right subtrees

        public Node(Key key, Value value) {
            this.key   = key;
            this.value = value;
        }
    }

    public boolean contains(Key key) {
        return get(key) != null;
    }

    // return value associated with the given key
    // if no such value, return null
    public Value get(Key key) {
        root = splay(root, key);
        int cmp = key.compareTo(root.key);
        if (cmp == 0) return root.value;
        else          return null;
    }    

   /***************************************************************************
    *  Splay tree insertion.
    ***************************************************************************/
    public void put(Key key, Value value) {
        // splay key to root
        if (root == null) {
            root = new Node(key, value);
            return;
        }
        
        root = splay(root, key);

        int cmp = key.compareTo(root.key);
        
        // Insert new node at root
        if (cmp < 0) {
            Node n = new Node(key, value);
            n.left = root.left;
            n.right = root;
            root.left = null;
            root = n;
        }

        // Insert new node at root
        else if (cmp > 0) {
            Node n = new Node(key, value);
            n.right = root.right;
            n.left = root;
            root.right = null;
            root = n;
        }

        // It was a duplicate key. Simply replace the value
        else {
            root.value = value;
        }

    }
    
   /***************************************************************************
    *  Splay tree deletion.
    ***************************************************************************/
    /* This splays the key, then does a slightly modified Hibbard deletion on
     * the root (if it is the node to be deleted; if it is not, the key was 
     * not in the tree). The modification is that rather than swapping the
     * root (call it node A) with its successor, it's successor (call it Node B)
     * is moved to the root position by splaying for the deletion key in A's 
     * right subtree. Finally, A's right child is made the new root's right 
     * child.
     */
    public void remove(Key key) {
        if (root == null) return; // empty tree
        
        root = splay(root, key);

        int cmp = key.compareTo(root.key);
        
        if (cmp == 0) {
            if (root.left == null) {
                root = root.right;
            } 
            else {
                Node x = root.right;
                root = root.left;
                splay(root, key);
                root.right = x;
            }
        }

        // else: it wasn't in the tree to remove
    }
    
    
   /***************************************************************************
    * Splay tree function.
    * **********************************************************************/
    // splay key in the tree rooted at Node h. If a node with that key exists,
    //   it is splayed to the root of the tree. If it does not, the last node
    //   along the search path for the key is splayed to the root.
    private Node splay(Node h, Key key) {
        if (h == null) return null;

        int cmp1 = key.compareTo(h.key);

        if (cmp1 < 0) {
            // key not in tree, so we're done
            if (h.left == null) {
                return h;
            }
            int cmp2 = key.compareTo(h.left.key);
            if (cmp2 < 0) {
                h.left.left = splay(h.left.left, key);
                h = rotateRight(h);
            }
            else if (cmp2 > 0) {
                h.left.right = splay(h.left.right, key);
                if (h.left.right != null)
                    h.left = rotateLeft(h.left);
            }
            
            if (h.left == null) return h;
            else                return rotateRight(h);
        }

        else if (cmp1 > 0) { 
            // key not in tree, so we're done
            if (h.right == null) {
                return h;
            }

            int cmp2 = key.compareTo(h.right.key);
            if (cmp2 < 0) {
                h.right.left  = splay(h.right.left, key);
                if (h.right.left != null)
                    h.right = rotateRight(h.right);
            }
            else if (cmp2 > 0) {
                h.right.right = splay(h.right.right, key);
                h = rotateLeft(h);
            }
            
            if (h.right == null) return h;
            else                 return rotateLeft(h);
        }

        else return h;
    }


   /***************************************************************************
    *  Helper functions.
    ***************************************************************************/

    // height of tree (1-node tree has height 0)
    public int height() { return height(root); }
    private int height(Node x) {
        if (x == null) return -1;
        return 1 + Math.max(height(x.left), height(x.right));
    }

    
    public int size() {
        return size(root);
    }
    
    private int size(Node x) {
        if (x == null) return 0;
        else return 1 + size(x.left) + size(x.right);
    }
    
    // right rotate
    private Node rotateRight(Node h) {
        Node x = h.left;
        h.left = x.right;
        x.right = h;
        return x;
    }

    // left rotate
    private Node rotateLeft(Node h) {
        Node x = h.right;
        h.right = x.left;
        x.left = h;
        return x;
    }

    // test client
    public static void main(String[] args) {
        SplayBST<Integer, Integer> st1 = new SplayBST<Integer, Integer>();
        st1.put(5, 5);
        st1.put(9, 9);
        st1.put(13, 13);
        st1.put(11, 11);
        st1.put(1, 1);
        
        
        SplayBST<String, String> st = new SplayBST<String, String>();
        st.put("www.cs.princeton.edu", "128.112.136.11");
        st.put("www.cs.princeton.edu", "128.112.136.12");
        st.put("www.cs.princeton.edu", "128.112.136.13");
        st.put("www.princeton.edu",    "128.112.128.15");
        st.put("www.yale.edu",         "130.132.143.21");
        st.put("www.simpsons.com",     "209.052.165.60");
        StdOut.println("The size 0 is: " + st.size());
        st.remove("www.yale.edu");
        StdOut.println("The size 1 is: " + st.size());
        st.remove("www.princeton.edu");
        StdOut.println("The size 2 is: " + st.size());
        st.remove("non-member");
        StdOut.println("The size 3 is: " + st.size());
        StdOut.println(st.get("www.cs.princeton.edu"));
        StdOut.println("The size 4 is: " + st.size());
        StdOut.println(st.get("www.yale.com"));
        StdOut.println("The size 5 is: " + st.size());
        StdOut.println(st.get("www.simpsons.com"));
        StdOut.println("The size 6 is: " + st.size());
        StdOut.println();
    }

}


Copyright © 2000–2017, Robert Sedgewick and Kevin Wayne.
Last updated: Fri Oct 20 12:50:46 EDT 2017.