ArrayST.java


Below is the syntax highlighted version of ArrayST.java from §3.1 Elementary Symbol Tables.


/******************************************************************************
 *  Compilation:  javac ArrayST.java
 *  Execution:    java ArrayST < input.txt
 *  Dependencies: StdIn.java StdOut.java
 *  Data files:   https://algs4.cs.princeton.edu/31elementary/tinyST.txt
 *  
 *  
 *  Symbol table implementation with unordered array. Uses repeated
 *  doubling to resize the array.
 *
 *  % java ArrayST < tiny.txt 
 *  S 0
 *  H 5
 *  X 7
 *  R 3
 *  C 4
 *  L 11
 *  A 8
 *  M 9
 *  P 10
 *  E 12
 *
 ******************************************************************************/

public class ArrayST<Key, Value> {
    private static final int INIT_SIZE = 8;

    private Value[] vals;   // symbol table values
    private Key[] keys;     // symbol table keys
    private int n = 0;      // number of elements in symbol table

    public ArrayST() {
        keys = (Key[])   new Object[INIT_SIZE];
        vals = (Value[]) new Object[INIT_SIZE];
    }

    // return the number of key-value pairs in the symbol table
    public int size() {
        return n;
    }

    // is the symbol table empty?
    public boolean isEmpty() {
        return size() == 0;
    }

    // resize the parallel arrays to the given capacity
    private void resize(int capacity) {
        Key[]   tempk = (Key[])   new Object[capacity];
        Value[] tempv = (Value[]) new Object[capacity];
        for (int i = 0; i < n; i++)
            tempk[i] = keys[i];
        for (int i = 0; i < n; i++)
            tempv[i] = vals[i];
        keys = tempk;
        vals = tempv;
    }

    // insert the key-value pair into the symbol table
    public void put(Key key, Value val) {

        // to deal with duplicates
        delete(key);

        // double size of arrays if necessary
        if (n >= vals.length) resize(2*n);

        // add new key and value at the end of array
        vals[n] = val;
        keys[n] = key;
        n++;
    }

    public Value get(Key key) {
        for (int i = 0; i < n; i++)
            if (keys[i].equals(key)) return vals[i];
        return null;
    }

    public Iterable<Key> keys() {
        Queue<Key> queue = new Queue<Key>();
        for (int i = 0; i < n; i++)
            queue.enqueue(keys[i]);
        return queue;
    }

    // remove given key (and associated value)
    public void delete(Key key) {
        for (int i = 0; i < n; i++) {
            if (key.equals(keys[i])) {
                keys[i] = keys[n-1];
                vals[i] = vals[n-1];
                keys[n-1] = null;
                vals[n-1] = null;
                n--;
                if (n > 0 && n == keys.length/4) resize(keys.length/2);
                return;
            }
        }
    } 




   /***************************************************************************
    * Test routine.
    ***************************************************************************/
    public static void main(String[] args) {
        ArrayST<String, Integer> st = new ArrayST<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));
    }
}


Copyright © 2000–2017, Robert Sedgewick and Kevin Wayne.
Last updated: Fri Oct 20 12:50:46 EDT 2017.