edu.princeton.cs.algorithms.SequentialSearchST Maven / Gradle / Ivy
Show all versions of algorithms Show documentation
package edu.princeton.cs.algorithms;
import edu.princeton.cs.introcs.StdIn;
import edu.princeton.cs.introcs.StdOut;
/*************************************************************************
* Compilation: javac SequentialSearchST.java
* Execution: java SequentialSearchST
* Dependencies: StdIn.java StdOut.java
* Data files: http://algs4.cs.princeton.edu/31elementary/tinyST.txt
*
* Symbol table implementation with sequential search in an
* unordered linked list of key-value pairs.
*
* % more tinyST.txt
* S E A R C H E X A M P L E
*
* % java SequentialSearchST < tiny.txt
* L 11
* P 10
* M 9
* X 7
* H 5
* C 4
* R 3
* A 8
* E 12
* S 0
*
*************************************************************************/
/**
* The SequentialSearchST class represents an (unordered)
* symbol table of generic key-value pairs.
* It supports the usual put, get, contains,
* delete, size, and is-empty methods.
* It also provides a keys method for iterating over all of the keys.
* A symbol table implements the associative array 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.
* The class also uses the convention that values cannot be null. Setting the
* value associated with a key to null is equivalent to deleting the key
* from the symbol table.
*
* This implementation uses a singly-linked list and sequential search.
* It relies on the equals() method to test whether two keys
* are equal. It does not call either the compareTo() or
* hashCode() method.
* The put and delete operations take linear time; the
* get and contains operations takes linear time in the worst case.
* The size, and is-empty operations take constant time.
* Construction takes constant time.
*
* For additional documentation, see Section 3.1 of
* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class SequentialSearchST {
private int N; // number of key-value pairs
private Node first; // the linked list of key-value pairs
// a helper linked list data type
private class Node {
private Key key;
private Value val;
private Node next;
public Node(Key key, Value val, Node next) {
this.key = key;
this.val = val;
this.next = next;
}
}
/**
* Initializes an empty symbol table.
*/
public SequentialSearchST() {
}
/**
* 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;
}
/**
* Is this symbol table empty?
* @return true if this symbol table is empty and false otherwise
*/
public boolean isEmpty() {
return size() == 0;
}
/**
* Does this symbol table contain the given key?
* @param key the key
* @return true if this symbol table contains key and
* false otherwise
*/
public boolean contains(Key key) {
return get(key) != null;
}
/**
* Returns the value associated with the given key.
* @param key the key
* @return the value associated with the given key if the key is in the symbol table
* and null if the key is not in the symbol table
*/
public Value get(Key key) {
for (Node x = first; x != null; x = x.next) {
if (key.equals(x.key)) return x.val;
}
return null;
}
/**
* Inserts the key-value pair into the symbol table, overwriting the old value
* with the new value if the key is already in the symbol table.
* If the value is null, this effectively deletes the key from the symbol table.
* @param key the key
* @param val the value
*/
public void put(Key key, Value val) {
if (val == null) { delete(key); return; }
for (Node x = first; x != null; x = x.next)
if (key.equals(x.key)) { x.val = val; return; }
first = new Node(key, val, first);
N++;
}
/**
* Removes the key and associated value from the symbol table
* (if the key is in the symbol table).
* @param key the key
*/
public void delete(Key key) {
first = delete(first, key);
}
// delete key in linked list beginning at Node x
// warning: function call stack too large if table is large
private Node delete(Node x, Key key) {
if (x == null) return null;
if (key.equals(x.key)) { N--; return x.next; }
x.next = delete(x.next, key);
return x;
}
/**
* Returns all keys in the symbol table as an Iterable.
* To iterate over all of the keys in the symbol table named st,
* use the foreach notation: for (Key key : st.keys()).
* @return all keys in the sybol table as an Iterable
*/
public Iterable keys() {
Queue queue = new Queue();
for (Node x = first; x != null; x = x.next)
queue.enqueue(x.key);
return queue;
}
/**
* Unit tests the SequentialSearchST data type.
*/
public static void main(String[] args) {
SequentialSearchST st = new SequentialSearchST();
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));
}
}