package edu.princeton.cs.algs4.ch34;
import edu.princeton.cs.algs4.ch13.Queue;
import edu.princeton.cs.algs4.ch31.SequentialSearchST;
import edu.princeton.cs.introcs.*;
/*************************************************************************
* Compilation: javac SeparateChainingHashST.java
* Execution: java SeparateChainingHashST
*
* A symbol table implemented with a separate-chaining hash table.
*
* % java SeparateChainingHashST
*
*************************************************************************/
public class SeparateChainingHashST<Key, Value> {
private static final int INIT_CAPACITY = 4;
// largest prime <= 2^i for i = 3 to 31
// not currently used for doubling and shrinking
// private static final int[] PRIMES = {
// 7, 13, 31, 61, 127, 251, 509, 1021, 2039, 4093, 8191, 16381,
// 32749, 65521, 131071, 262139, 524287, 1048573, 2097143, 4194301,
// 8388593, 16777213, 33554393, 67108859, 134217689, 268435399,
// 536870909, 1073741789, 2147483647
// };
private int N; // number of key-value pairs
private int M; // hash table size
private SequentialSearchST<Key, Value>[] st; // array of linked-list symbol tables
// create separate chaining hash table
public SeparateChainingHashST() {
this(INIT_CAPACITY);
}
// create separate chaining hash table with M lists
public SeparateChainingHashST(int M) {
this.M = M;
st = (SequentialSearchST<Key, Value>[]) new SequentialSearchST[M];
for (int i = 0; i < M; i++)
st[i] = new SequentialSearchST<Key, Value>();
}
// resize the hash table to have the given number of chains b rehashing all of the keys
private void resize(int chains) {
SeparateChainingHashST<Key, Value> temp = new SeparateChainingHashST<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;
}
// return number of key-value pairs in symbol table
public int size() {
return N;
}
// is the symbol table empty?
public boolean isEmpty() {
return size() == 0;
}
// is the key in the symbol table?
public boolean contains(Key key) {
return get(key) != null;
}
// return value associated with key, null if no such key
public Value get(Key key) {
int i = hash(key);
return st[i].get(key);
}
// insert key-value pair into the table
public void put(Key key, Value val) {
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);
}
// delete key (and associated value) if key is in the table
public void delete(Key key) {
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 test client.
***********************************************************************/
public static void main(String[] args) {
SeparateChainingHashST<String, Integer> st = new SeparateChainingHashST<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));
}
}
/*************************************************************************
* Copyright 2002-2012, Robert Sedgewick and Kevin Wayne.
*
* This file is part of algs4-package.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-package.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-package.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-package.jar. If not, see http://www.gnu.org/licenses.
*************************************************************************/