SequentialSearchST.java

Below is the syntax highlighted version of SequentialSearchST.java from §3.4 Hash Tables.

/******************************************************************************
 *  Compilation:  javac SequentialSearchST.java
 *  Execution:    java SequentialSearchST
 *  Dependencies: StdIn.java StdOut.java
 *  Data files:   https://algs4.cs.princeton.edu/31elementary/tinyST.txt  
 *  
 *  Symbol table implementation with sequential search in an
 *  unordered linked list of key-value pairs.
 *
 *  % more tinyST.txt
 *  S E A R C H E X A M P L E
 *
 *  % java SequentialSearchST < tiny.txt 
 *  L 11
 *  P 10
 *  M 9
 *  X 7
 *  H 5
 *  C 4
 *  R 3
 *  A 8
 *  E 12
 *  S 0
 *
 ******************************************************************************/

/**
 *  The {@code SequentialSearchST} class represents an (unordered)
 *  symbol table of generic key-value pairs.
 *  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 a <em>keys</em> method for iterating over all of the keys.
 *  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.
 *  The class also 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 singly-linked list and sequential search.
 *  It relies on the {@code equals()} method to test whether two keys
 *  are equal. It does not call either the {@code compareTo()} or
 *  {@code hashCode()} method. 
 *  The <em>put</em> and <em>delete</em> operations take linear time; the
 *  <em>get</em> and <em>contains</em> operations takes linear time in the worst case.
 *  The <em>size</em>, and <em>is-empty</em> operations take constant time.
 *  Construction takes constant time.
 *  <p>
 *  For additional documentation, see <a href="https://algs4.cs.princeton.edu/31elementary">Section 3.1</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 */
public class SequentialSearchST<Key, Value> {
    private int n;           // number of key-value pairs
    private Node first;      // the linked list of key-value pairs

    // a helper linked list data type
    private class Node {
        private Key key;
        private Value val;
        private Node next;

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

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

    /**
     * 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;
    }

    /**
     * Is this symbol table empty?
     * @return {@code true} if this symbol table is empty and {@code false} otherwise
     */
    public boolean isEmpty() {
        return size() == 0;
    }

    /**
     * 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
     */
    public boolean contains(Key key) {
        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
     */
    public Value get(Key key) {
        for (Node x = first; x != null; x = x.next) {
            if (key.equals(x.key))
                return x.val;
        }
        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 {@code null}, this effectively deletes the key from the symbol table.
     * @param key the key
     * @param val the value
     */
    public void put(Key key, Value val) {
        if (val == null) {
            delete(key);
            return;
        }

        for (Node x = first; x != null; x = x.next) {
            if (key.equals(x.key)) {
                x.val = val;
                return;
            }
        }
        first = new Node(key, val, first);
        n++;
    }

    /**
     * Removes the key and associated value from the symbol table
     * (if the key is in the symbol table).
     * @param key the key
     */
    public void delete(Key key) {
        first = delete(first, key);
    }

    // delete key in linked list beginning at Node x
    // warning: function call stack too large if table is large
    private Node delete(Node x, Key key) {
        if (x == null) return null;
        if (key.equals(x.key)) {
            n--;
            return x.next;
        }
        x.next = delete(x.next, key);
        return x;
    }


    /**
     * Returns all keys in the symbol table as an {@code Iterable}.
     * To iterate over all of the keys in the symbol table named {@code st},
     * use the foreach notation: {@code for (Key key : st.keys())}.
     * @return all keys in the symbol table as an {@code Iterable}
     */
    public Iterable<Key> keys()  {
        Queue<Key> queue = new Queue<Key>();
        for (Node x = first; x != null; x = x.next)
            queue.enqueue(x.key);
        return queue;
    }


    /**
     * Unit tests the {@code SequentialSearchST} data type.
     *
     * @param args the command-line arguments
     */
    public static void main(String[] args) {
        SequentialSearchST<String, Integer> st = new SequentialSearchST<String, Integer>();
        for (int i = 0; !StdIn.isEmpty(); i++) {
            String key = StdIn.readString();
            st.put(key, i);
        }
        for (String s : st.keys())
            StdOut.println(s + " " + st.get(s));
    }
}