LinearProbingHashST.cs
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using System; using System.Collections.Generic; using System.Diagnostics; using System.Linq; using System.Text; using System.Threading.Tasks; namespace LinearProbingHashST { class LinearProbingHashST<Key,Value> { private int INIT_CAPACITY = 4; public int n; // number of key-value pairs in the symbol table public int m; // size of linear probing table public Key[] keys; // the keys public Value[] vals; // the values /** * Initializes an empty symbol table. */ public LinearProbingHashST() { m = INIT_CAPACITY; n = 0; keys = new Key[m]; vals = new Value[m]; } /** * Initializes an empty symbol table with the specified initial capacity. * * @param capacity the initial capacity */ public LinearProbingHashST(int capacity) { m = capacity; n = 0; keys = new Key[m]; vals = new Value[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 bool 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 bool contains(Key key) { if (key == null) throw new ArgumentException("argument to contains() is null"); return get(key) != null; } // hash function for keys - returns value between 0 and M-1 private int hash(Key key) { return (key.GetHashCode() & 0x7fffffff) % m; } // 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 ArgumentException("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 ArgumentException("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 default(Value); } /** * 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 ArgumentException("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] = default(Key); vals[i] = default(Value); // 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] = default(Key); vals[i] = default(Value); 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); Trace.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 IEnumerable<Key> allkeys() { Queue<Key> queue = new Queue<Key>(); for (int i = 0; i < m; i++) if (keys[i] != null) queue.Enqueue(keys[i]); return queue; } public void ConsoleDisplay() { Console.WriteLine("key" + " " + "val"); for (int i = 0; i < m; i++) { if (keys[i] != null) Console.WriteLine(" " + keys[i] + " " + vals[i]); } } // integrity check - don't check after each put() because // integrity not maintained during a delete() private bool check() { // check that hash table is at most 50% full if (m < 2 * n) { Console.WriteLine("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]).Equals(vals[i])) { Console.WriteLine("get[" + keys[i] + "] = " + get(keys[i]) + "; vals[i] = " + vals[i]); return false; } } return true; } } } |
Test
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using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace LinearProbingHashST { class Program { static void Main(string[] args) { LinearProbingHashST<string, int> lp = new LinearProbingHashST<string, int>(16); string[] a = { "S", "E", "A", "R", "C", "H", "E", "X", "A", "M", "P", "L", "E" }; for (int i = 0; i < a.Length; i++) { lp.put(a[i], i); } lp.ConsoleDisplay(); Console.ReadLine(); } } } |