/*************************************************************************
* Compilation: javac ST.java
* Execution: java ST
*
* Sorted symbol table implementation using a java.util.TreeMap.
* Does not allow duplicates.
*
* % java ST
*
*************************************************************************/
// This modified version by Will Gwozdz to make it visualizable!
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.SortedMap;
import java.util.Set;
import java.util.TreeSet;
/**
* The ST class represents an ordered symbol table of generic
* key-value pairs.
* It supports the usual put, get, contains,
* delete, size, and is-empty methods.
* It also provides ordered methods for finding the minimum,
* maximum, floor, and ceiling.
* It also provides a keys method for iterating over all of the keys.
* A symbol table implements the associative array abstraction:
* when associating a value with a key that is already in the symbol table,
* the convention is to replace the old value with the new value.
* Unlike {@link java.util.Map}, this class uses the convention that
* values cannot be null—setting the
* value associated with a key to null is equivalent to deleting the key
* from the symbol table.
*
* This implementation uses a balanced binary search tree. It requires that
* the key type implements the Comparable interface and calls the
* compareTo() and method to compare two keys. It does not call either
* equals() or hashCode().
* The put, contains, remove, minimum,
* maximum, ceiling, and floor operations each take
* logarithmic time in the worst case.
* The size, and is-empty operations take constant time.
* Construction takes constant time.
*
* For additional documentation, see Section 4.4 of
* Introduction to Programming in Java: An Interdisciplinary Approach by Robert Sedgewick and Kevin Wayne.
*/
public class ST, Value> implements Iterable {
private class Node {
Key key;
Value value;
Node left;
Node right;
}
private Node first;
/**
* Returns the value associated with the given key.
* @param key the key
* @return the value associated with the given key if the key is in the symbol table
* and null if the key is not in the symbol table
* @throws NullPointerException if key is null
*/
public Value get(Key key) {
if (key == null) throw new NullPointerException("called get() with null key");
Node n = first;
while (n != null) {
if (key.compareTo(n.key) < 0)
n = n.left;
else if (key.compareTo(n.key) > 0)
n = n.right;
else
return n.value;
}
return null;
}
/**
* Inserts the key-value pair into the symbol table, overwriting the old value
* with the new value if the key is already in the symbol table.
* If the value is null, this effectively deletes the key from the symbol table.
* @param key the key
* @param val the value
* @throws NullPointerException if key is null
*/
public void put(Key key, Value val) {
if (key == null) throw new NullPointerException("called put() with null key");
//if (val == null) return delete(key); // restore this once delete is implemented.
Node add = new Node();
add.key = key;
add.value = val;
if (first == null)
first = add;
else {
Node n = first;
while (true) {
if (key.compareTo(n.key) < 0) {
if (n.left == null) {
n.left = add;
return;
}
n = n.left;
}
else if (key.compareTo(n.key) > 0) {
if (n.right == null) {
n.right = add;
return;
}
n = n.right;
}
else {
n.value = val;
return;
}
}
}
}
/**
* Removes the key and associated value from the symbol table
* (if the key is in the symbol table).
* @param key the key
* @throws NullPointerException if key is null
*/
public void delete(Key key) {
if (key == null) throw new NullPointerException("called delete() with null key");
put(key, null); // simply put a null value for now. a node with a null value counts as deleted.
}
/**
* Does this symbol table contain the given key?
* @param key the key
* @return true if this symbol table contains key and
* false otherwise
* @throws NullPointerException if key is null
*/
public boolean contains(Key key) {
if (key == null) throw new NullPointerException("called contains() with null key");
return (get(key) != null);
}
/**
* Returns the number of key-value pairs in this symbol table.
* @return the number of key-value pairs in this symbol table
*/
public int size() {
return rCounter(first);
}
private int rCounter(Node n) {
if (n == null || n.value == null) return 0;
else return (1+rCounter(n.left)+rCounter(n.right));
}
/**
* Is this symbol table empty?
* @return true if this symbol table is empty and false otherwise
*/
public boolean isEmpty() {
return size() == 0;
}
/**
* Returns all keys in the symbol table as an Iterable.
* To iterate over all of the keys in the symbol table named st,
* use the foreach notation: for (Key key : st.keys()).
* @return all keys in the sybol table as an Iterable
*/
public Iterable keys() {
Set keys = new TreeSet();
return rKeys(keys, first);
}
private Set rKeys(Set keys, Node n) {
if (n != null) {
rKeys(keys, n.right);
if (n.value != null)
keys.add(n.key);
rKeys(keys, n.left);
}
return keys;
}
/**
* Returns all of the keys in the symbol table as an iterator.
* To iterate over all of the keys in a symbol table named st, use the
* foreach notation: for (Key key : st).
* @return an iterator to all of the keys in the symbol table
*/
public Iterator iterator() {
return keys().iterator();
}
/**
* Returns the smallest key in the symbol table.
* @return the smallest key in the symbol table
* @throws NoSuchElementException if the symbol table is empty
*/
public Key min() {
if (isEmpty()) throw new NoSuchElementException("called min() with empty symbol table");
Node n = first;
while (n.left != null)
n = n.left;
return n.key;
}
/**
* Returns the largest key in the symbol table.
* @return the largest key in the symbol table
* @throws NoSuchElementException if the symbol table is empty
*/
public Key max() {
if (isEmpty()) throw new NoSuchElementException("called max() with empty symbol table");
Node n = first;
while (n.right != null)
n = n.right;
return n.key;
}
/**
* Returns the smallest key in the symbol table greater than or equal to key.
* @return the smallest key in the symbol table greater than or equal to key
* @param key the key
* @throws NoSuchElementException if the symbol table is empty
* @throws NullPointerException if key is null
*/
public Key ceil(Key key) {
if (key == null) throw new NullPointerException("called ceil() with null key");
throw new RuntimeException("didnt bother inplementing ceil yet");
}
/**
* Returns the largest key in the symbol table less than or equal to key.
* @return the largest key in the symbol table less than or equal to key
* @param key the key
* @throws NoSuchElementException if the symbol table is empty
* @throws NullPointerException if key is null
*/
public Key floor(Key key) {
if (key == null) throw new NullPointerException("called floor() with null key");
throw new RuntimeException("didnt bother inplementing ceil yet");
}
/**
* Unit tests the ST data type.
*/
public static void main(String[] args) {
ST st = new ST();
// insert some key-value pairs
st.put("www.cs.princeton.edu", "128.112.136.11");
st.put("www.cs.princeton.edu", "128.112.136.35"); // overwrite old value
st.put("www.princeton.edu", "128.112.130.211");
st.put("www.math.princeton.edu", "128.112.18.11");
st.put("www.yale.edu", "130.132.51.8");
st.put("www.amazon.com", "207.171.163.90");
st.put("www.simpsons.com", "209.123.16.34");
st.put("www.stanford.edu", "171.67.16.120");
st.put("www.google.com", "64.233.161.99");
st.put("www.ibm.com", "129.42.16.99");
st.put("www.apple.com", "17.254.0.91");
st.put("www.slashdot.com", "66.35.250.150");
st.put("www.whitehouse.gov", "204.153.49.136");
st.put("www.espn.com", "199.181.132.250");
st.put("www.snopes.com", "66.165.133.65");
st.put("www.movies.com", "199.181.132.250");
st.put("www.cnn.com", "64.236.16.20");
st.put("www.iitb.ac.in", "202.68.145.210");
StdOut.println(st.get("www.cs.princeton.edu"));
StdOut.println(st.get("www.harvardsucks.com"));
StdOut.println(st.get("www.simpsons.com"));
StdOut.println();
StdOut.println("ceil(www.simpsonr.com) = " + st.ceil("www.simpsonr.com"));
StdOut.println("ceil(www.simpsons.com) = " + st.ceil("www.simpsons.com"));
StdOut.println("ceil(www.simpsont.com) = " + st.ceil("www.simpsont.com"));
StdOut.println("floor(www.simpsonr.com) = " + st.floor("www.simpsonr.com"));
StdOut.println("floor(www.simpsons.com) = " + st.floor("www.simpsons.com"));
StdOut.println("floor(www.simpsont.com) = " + st.floor("www.simpsont.com"));
StdOut.println();
StdOut.println("min key: " + st.min());
StdOut.println("max key: " + st.max());
StdOut.println("size: " + st.size());
StdOut.println();
// print out all key-value pairs in lexicographic order
for (String s : st.keys())
StdOut.println(s + " " + st.get(s));
}
}