Below is the syntax highlighted version of LinearProbingHashST.java
from §3.4 Hash Tables.
/****************************************************************************** * Compilation: javac LinearProbingHashST.java * Execution: java LinearProbingHashST < input.txt * Dependencies: StdIn.java StdOut.java * Data files: https://algs4.cs.princeton.edu/34hash/tinyST.txt * * Symbol-table implementation with linear-probing hash table. * ******************************************************************************/ /** * The {@code LinearProbingHashST} class represents a 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. * 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 linear probing hash table. It requires that * the key type overrides the {@code equals()} and {@code hashCode()} methods. * The expected time per <em>put</em>, <em>contains</em>, or <em>remove</em> * operation is constant, subject to the uniform hashing assumption. * 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/34hash">Section 3.4</a> of * <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne. * For other implementations, see {@link ST}, {@link BinarySearchST}, * {@link SequentialSearchST}, {@link BST}, {@link RedBlackBST}, and * {@link SeparateChainingHashST}, * * @author Robert Sedgewick * @author Kevin Wayne */ public class LinearProbingHashST<Key, Value> { // must be a power of 2 private static final int INIT_CAPACITY = 4; private int n; // number of key-value pairs in the symbol table private int m; // size of linear probing table private Key[] keys; // the keys private Value[] vals; // the values /** * Initializes an empty symbol table. */ public LinearProbingHashST() { this(INIT_CAPACITY); } /** * Initializes an empty symbol table with the specified initial capacity. * * @param capacity the initial capacity */ public LinearProbingHashST(int capacity) { m = capacity; n = 0; keys = (Key[]) new Object[m]; vals = (Value[]) new Object[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; } // hash function for keys - returns value between 0 and m-1 private int hashTextbook(Key key) { return (key.hashCode() & 0x7fffffff) % m; } // hash function for keys - returns value between 0 and m-1 (assumes m is a power of 2) // (from Java 7 implementation, protects against poor quality hashCode() implementations) private int hash(Key key) { int h = key.hashCode(); h ^= (h >>> 20) ^ (h >>> 12) ^ (h >>> 7) ^ (h >>> 4); return h & (m-1); } // resizes the hash table to the given capacity by re-hashing all of the keys private void resize(int capacity) { LinearProbingHashST<Key, Value> temp = new LinearProbingHashST<Key, Value>(capacity); for (int i = 0; i < m; i++) { if (keys[i] != null) { temp.put(keys[i], vals[i]); } } keys = temp.keys; vals = temp.vals; m = temp.m; } /** * 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 50% full if (n >= m/2) resize(2*m); int i; for (i = hash(key); keys[i] != null; i = (i + 1) % m) { if (keys[i].equals(key)) { vals[i] = val; return; } } keys[i] = key; vals[i] = val; n++; } /** * Returns the value associated with the specified key. * @param key the key * @return the value associated with {@code key}; * {@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"); for (int i = hash(key); keys[i] != null; i = (i + 1) % m) if (keys[i].equals(key)) return vals[i]; return null; } /** * 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"); if (!contains(key)) return; // find position i of key int i = hash(key); while (!key.equals(keys[i])) { i = (i + 1) % m; } // delete key and associated value keys[i] = null; vals[i] = null; // rehash all keys in same cluster i = (i + 1) % m; while (keys[i] != null) { // delete keys[i] and vals[i] and reinsert Key keyToRehash = keys[i]; Value valToRehash = vals[i]; keys[i] = null; vals[i] = null; n--; put(keyToRehash, valToRehash); i = (i + 1) % m; } n--; // halves size of array if it's 12.5% full or less if (n > 0 && n <= m/8) resize(m/2); assert check(); } /** * Returns all keys in this 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 this symbol table */ public Iterable<Key> keys() { Queue<Key> queue = new Queue<Key>(); for (int i = 0; i < m; i++) if (keys[i] != null) queue.enqueue(keys[i]); return queue; } // integrity check - don't check after each put() because // integrity not maintained during a call to delete() private boolean check() { // check that hash table is at most 50% full if (m < 2*n) { System.err.println("Hash table size m = " + m + "; array size n = " + n); return false; } // check that each key in table can be found by get() for (int i = 0; i < m; i++) { if (keys[i] == null) continue; else if (get(keys[i]) != vals[i]) { System.err.println("get[" + keys[i] + "] = " + get(keys[i]) + "; vals[i] = " + vals[i]); return false; } } return true; } /** * Unit tests the {@code LinearProbingHashST} data type. * * @param args the command-line arguments */ public static void main(String[] args) { LinearProbingHashST<String, Integer> st = new LinearProbingHashST<String, Integer>(); for (int i = 0; !StdIn.isEmpty(); i++) { String key = StdIn.readString(); st.put(key, i); } // print keys for (String s : st.keys()) StdOut.println(s + " " + st.get(s)); } }