rbhst.java

package heima9;
import edu.princeton.cs.algs4.*;

public class RedBlackHashST<Key extends Comparable<Key>, Value> {
    private static final int INIT_CAPACITY = 4;

    private int n;                                // number of key-value pairs
    private int m;                                // hash table size
    private RedBlackBST<Key, Value>[] st;  // array of linked-list symbol tables


    /**
     * Initializes an empty symbol table.
     */
    public RedBlackHashST() {
        this(INIT_CAPACITY);
    }

    /**
     * Initializes an empty symbol table with {@code m} chains.
     * @param m the initial number of chains
     */
    //@SuppressWarnings("unchecked")
    public RedBlackHashST(int m) {
        this.m = m;
        st = (RedBlackBST<Key, Value>[]) new RedBlackBST[m];
        for (int i = 0; i < m; i++)
            st[i] = new RedBlackBST<Key, Value>();
    }

    // resize the hash table to have the given number of chains,
    // rehashing all of the keys
    private void resize(int chains) {
        RedBlackHashST<Key, Value> temp = new RedBlackHashST<Key, Value>(chains);
        for (int i = 0; i < m; i++) {
            for (Key key : st[i].keys()) {
                temp.put(key, st[i].get(key));
            }
        }
        this.m  = temp.m;
        this.n  = temp.n;
        this.st = temp.st;
    }

    // hash value between 0 and m-1
    private int hash(Key key) {
        return (key.hashCode() & 0x7fffffff) % m;
    }

    /**
     * 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;
    }

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

    /**
     * Returns true if this symbol table contains the specified key.
     *
     * @param  key the key
     * @return {@code true} if this symbol table contains {@code key};
     *         {@code false} otherwise
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public boolean contains(Key key) {
        if (key == null) throw new IllegalArgumentException("argument to contains() is null");
        return get(key) != null;
    }

    /**
     * Returns the value associated with the specified key in this symbol table.
     *
     * @param  key the key
     * @return the value associated with {@code key} in the symbol table;
     *         {@code null} if no such value
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public Value get(Key key) {
        if (key == null) throw new IllegalArgumentException("argument to get() is null");
        int i = hash(key);
        return st[i].get(key);
    }

    /**
     * Inserts the specified key-value pair into the symbol table, overwriting the old
     * value with the new value if the symbol table already contains the specified key.
     * Deletes the specified key (and its associated value) from this symbol table
     * if the specified value is {@code null}.
     *
     * @param  key the key
     * @param  val the value
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public void put(Key key, Value val) {
        if (key == null) throw new IllegalArgumentException("first argument to put() is null");
        if (val == null) {
            delete(key);
            return;
        }

        // double table size if average length of list >= 10
        if (n >= 10*m) resize(2*m);

        int i = hash(key);
        if (!st[i].contains(key)) n++;
        st[i].put(key, val);
    }

    /**
     * Removes the specified key and its associated value from this symbol table
     * (if the key is in this symbol table).
     *
     * @param  key the key
     * @throws IllegalArgumentException if {@code key} is {@code null}
     */
    public void delete(Key key) {
        if (key == null) throw new IllegalArgumentException("argument to delete() is null");

        int i = hash(key);
        if (st[i].contains(key)) n--;
        st[i].delete(key);

        // halve table size if average length of list <= 2
        if (m > INIT_CAPACITY && n <= 2*m) resize(m/2);
    }

    // return keys in symbol table as an Iterable
    public Iterable<Key> keys() {
        Queue<Key> queue = new Queue<Key>();
        for (int i = 0; i < m; i++) {
            for (Key key : st[i].keys())
                queue.enqueue(key);
        }
        return queue;
    }


    /**
     * Unit tests the {@code SeparateChainingHashST} data type.
     *
     * @param args the command-line arguments
     */
    public static void main(String[] args) {
        RedBlackHashST<String, Integer> rbh = new RedBlackHashST<String, Integer>();
        for (int i = 0; !StdIn.isEmpty(); i++) {
            String key = StdIn.readString();
            rbh.put(key, i);
        }

        // print keys
        for (String s : rbh.keys())
            StdOut.println(s + " " + rbh.get(s));

    }

}