package edu.princeton.cs.algs4.ch34;
import edu.princeton.cs.algs4.ch13.Queue;
import edu.princeton.cs.introcs.*;
/*************************************************************************
* Compilation: javac LinearProbingHashST.java
* Execution: java LinearProbingHashST
*
* Symbol table implementation with linear probing hash table.
*
* % java LinearProbingHashST
* 128.112.136.11
* 208.216.181.15
* null
*
*
*************************************************************************/
public class LinearProbingHashST<Key, Value> {
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
// create an empty hash table - use 16 as default size
public LinearProbingHashST() {
this(INIT_CAPACITY);
}
// create linear proving hash table of given capacity
public LinearProbingHashST(int capacity) {
M = capacity;
keys = (Key[]) new Object[M];
vals = (Value[]) new Object[M];
}
// 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;
}
// does a key-value pair with the given key exist in the symbol table?
public boolean contains(Key key) {
return get(key) != null;
}
// hash function for keys - returns value between 0 and M-1
private int hash(Key key) {
return (key.hashCode() & 0x7fffffff) % M;
}
// resize 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;
}
// insert the key-value pair into the symbol table
public void put(Key key, Value val) {
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++;
}
// return the value associated with the given key, null if no such value
public Value get(Key key) {
for (int i = hash(key); keys[i] != null; i = (i + 1) % M)
if (keys[i].equals(key))
return vals[i];
return null;
}
// delete the key (and associated value) from the symbol table
public void delete(Key key) {
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] an 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();
}
// return all of the keys as in Iterable
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 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 test client.
***********************************************************************/
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));
}
}
/*************************************************************************
* 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.
*************************************************************************/