content: /*************************************************************************
   *  Compilation:  javac ST.java
   *  Execution:    java ST
   *  
   *  Sorted symbol table implementation using a java.util.TreeMap.
   *  Does not allow duplicates.
   *
   *  % java ST
   *
   *************************************************************************/
  
  import java.util.Iterator;
  import java.util.SortedMap;
  import java.util.TreeMap;
  
  /**
   *  This class represents an ordered symbol table. It assumes that
   *  the elements are <tt>Comparable</tt>.
   *  It supports the usual <em>put</em>, <em>get</em>, <em>contains</em>,
   *  and <em>remove</em> methods.
   *  It also provides ordered methods for finding the <em>minimum</em>,
   *  <em>maximum</em>, <em>floor</em>, and <em>ceiling</em>.
   *  <p>
   *  The class uses the convention that values cannot be null. Setting the
   *  value associated with a key to null is equivalent to removing the key.
   *  <p>
   *  This class implements the Iterable interface for compatiblity with
   *  the version from <em>Introduction to Programming in Java: An Interdisciplinary
   *  Approach</em>.
   *  <p>
   *  This implementation uses a balanced binary search tree.
   *  The <em>add</em>, <em>contains</em>, <em>remove</em>, <em>minimum</em>,
   *  <em>maximum</em>, <em>ceiling</em>, and <em>floor</em> methods take
   *  logarithmic time.
   *  <p>
   *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/35applications">Section 4.5</a> of
   *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
   */
  public class ST<Key extends Comparable<Key>, Value> implements Iterable<Key> {
  
      private TreeMap<Key, Value> st;
  
      /**
       * Create an empty symbol table.
       */
      public ST() {
          st = new TreeMap<Key, Value>();
      }
  
      /**
       * Put key-value pair into the symbol table. Remove key from table if
       * value is null.
       */
      public void put(Key key, Value val) {
          if (val == null) st.remove(key);
          else             st.put(key, val);
      }
  
      /**
       * Return the value paired with given key; null if key is not in table.
       */
      public Value get(Key key) {
          return st.get(key);
      }
  
      /**
       * Delete the key (and paired value) from table.
       * Return the value paired with given key; null if key is not in table.
       */
      public Value delete(Key key) {
          return st.remove(key);
      }
  
      /**
       * Is the key in the table?
       */
      public boolean contains(Key key) {
          return st.containsKey(key);
      }
  
      /**
       * How many keys are in the table?
       */
      public int size() {
          return st.size();
      }
  
      /**
       * Return an <tt>Iterable</tt> for the keys in the table.
       * To iterate over all of the keys in the symbol table <tt>st</tt>, use the
       * foreach notation: <tt>for (Key key : st.keys())</tt>.
       */ 
      public Iterable<Key> keys() {
          return st.keySet();
      }
  
     /**
       * Return an <tt>Iterator</tt> for the keys in the table.
       * To iterate over all of the keys in the symbol table <tt>st</tt>, use the
       * foreach notation: <tt>for (Key key : st)</tt>.
       * This method is for backward compatibility with the version from <em>Introduction
       * to Programming in Java: An Interdisciplinary Approach.</em>
       */
      public Iterator<Key> iterator() {
          return st.keySet().iterator();
      }
  
      /**
       * Return the smallest key in the table.
       */ 
      public Key min() {
          return st.firstKey();
      }
  
      /**
       * Return the largest key in the table.
       */ 
      public Key max() {
          return st.lastKey();
      }
  
  
      /**
       * Return the smallest key in the table >= k.
       */ 
      public Key ceil(Key k) {
          SortedMap<Key, Value> tail = st.tailMap(k);
          if (tail.isEmpty()) return null;
          else return tail.firstKey();
      }
  
      /**
       * Return the largest key in the table <= k.
       */ 
      public Key floor(Key k) {
          if (st.containsKey(k)) return k;
  
          // does not include key if present (!)
          SortedMap<Key, Value> head = st.headMap(k);
          if (head.isEmpty()) return null;
          else return head.lastKey();
      }
  
     /***********************************************************************
      * Test routine.
      **********************************************************************/
      public static void main(String[] args) {
          ST<String, String> st = new ST<String, String>();
  
         // 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));
      }
  
  }
  