TSTmod.java

/******************************************************************************
 *  Compilation:  javac TSTmod.java
 *  Execution:    java TSTmod < words.txt
 *  Dependencies: StdIn.java
 *  Data files:   https://algs4.cs.princeton.edu/52trie/shellsST.txt
 *
 *  Symbol table with string keys, implemented using a ternary search
 *  trie (TST).
 *
 *
 *  % java TSTmod < shellsST.txt
 *  keys(""):
 *  by 4
 *  sea 6
 *  sells 1
 *  she 0
 *  shells 3
 *  shore 7
 *  the 5
 *
 *  longestPrefixOf("shellsort"):
 *  shells
 *
 *  keysWithPrefix("shor"):
 *  shore
 *
 *  keysThatMatch(".he.l."):
 *  shells
 *
 *  % java TSTmod
 *  theory the now is the time for all good men
 *
 *  Remarks
 *  --------
 *    - can't use a key that is the empty string ""
 *
 ******************************************************************************/
/**
 *  The {@code TSTmod} class represents an symbol table of key-value
 *  pairs, with string keys and generic values.
 *  It supports the usual <em>put</em>, <em>get</em>, <em>contains</em>,
 *  <em>delete</em>, <em>size</em>, and <em>is-empty</em> methods.
 *  It also provides character-based methods for finding the string
 *  in the symbol table that is the <em>longest prefix</em> of a given prefix,
 *  finding all strings in the symbol table that <em>start with</em> a given prefix,
 *  and finding all strings in the symbol table that <em>match</em> a given pattern.
 *  A symbol table implements the <em>associative array</em> 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 {@code null}—setting the
 *  value associated with a key to {@code null} is equivalent to deleting the key
 *  from the symbol table.
 *  <p>
 *  This implementation uses a ternary search trie.
 *  <p>
 *  For additional documentation, see <a href="https://algs4.cs.princeton.edu/52trie">Section 5.2</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 */
public class TSTmod<Value> {
    private int n;              // size
    private Node<Value> root;   // root of TST

    private static class Node<Value> {
        private char c;                        // character
        private Node<Value> left, mid, right;  // left, middle, and right subtries
        private Value val;                     // value associated with string
    }

    /**
     * Initializes an empty string symbol table.
     */
    public TSTmod() {
    }

    /**
     * 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 n;
    }

    /**
     * Does this symbol table contain the given key?
     * @param key the key
     * @return {@code true} if this symbol table contains {@code key} and
     *     {@code false} otherwise
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public boolean contains(StringBuilder key) {
        if (key == null) {
            throw new IllegalArgumentException("argument to contains() is null");
        }
        return get(key) != null;
    }

    /**
     * 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 {@code null} if the key is not in the symbol table
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public Value get(StringBuilder key) {
        if (key == null) {
            throw new IllegalArgumentException("calls get() with null argument");
        }
        if (key.length() == 0) throw new IllegalArgumentException("key must have length >= 1");
        Node<Value> x = get(root, key, 0);
        if (x == null) return null;
        return x.val;
    }

    // return subtrie corresponding to given key
    private Node<Value> get(Node<Value> x, StringBuilder key, int d) {
        if (x == null) return null;
        if (key.length() == 0) throw new IllegalArgumentException("key must have length >= 1");
        char c = key.charAt(d);
        if      (c < x.c)              return get(x.left,  key, d);
        else if (c > x.c)              return get(x.right, key, d);
        else if (d < key.length() - 1) return get(x.mid,   key, d+1);
        else                           return x;
    }

    /**
     * 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 {@code null}, this effectively deletes the key from the symbol table.
     * @param key the key
     * @param val the value
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public void put(StringBuilder key, Value val) {
        if (key == null) {
            throw new IllegalArgumentException("calls put() with null key");
        }
        if (!contains(key)) n++;
        root = put(root, key, val, 0);
    }

    private Node<Value> put(Node<Value> x, StringBuilder key, Value val, int d) {
        char c = key.charAt(d);
        if (x == null) {
            x = new Node<Value>();
            x.c = c;
        }
        if      (c < x.c)               x.left  = put(x.left,  key, val, d);
        else if (c > x.c)               x.right = put(x.right, key, val, d);
        else if (d < key.length() - 1)  x.mid   = put(x.mid,   key, val, d+1);
        else                            x.val   = val;
        return x;
    }


}

/******************************************************************************
 *  Copyright 2002-2018, Robert Sedgewick and Kevin Wayne.
 *
 *  This file is part of algs4.jar, which accompanies the textbook
 *
 *      Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
 *      Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
 *      http://algs4.cs.princeton.edu
 *
 *
 *  algs4.jar is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  algs4.jar is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with algs4.jar.  If not, see http://www.gnu.org/licenses.
 ******************************************************************************/