283 lines
8.8 KiB
Java
283 lines
8.8 KiB
Java
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/*************************************************************************
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* Compilation: javac TrieSET.java
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* Execution: java TrieSET < words.txt
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* Dependencies: StdIn.java
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*
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* An set for extended ASCII strings, implemented using a 256-way trie.
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*
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* Sample client reads in a list of words from standard input and
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* prints out each word, removing any duplicates.
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*
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*************************************************************************/
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import java.util.Iterator;
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import edu.princeton.cs.introcs.StdIn;
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import edu.princeton.cs.introcs.StdOut;
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/**
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* The TrieSET class represents an ordered set of strings over
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* the extended ASCII alphabet.
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* It supports the usual add , contains , and delete
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* methods. It also provides character-based methods for finding the string
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* in the set that is the longest prefix of a given prefix,
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* finding all strings in the set that start with a given prefix,
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* and finding all strings in the set that match a given pattern.
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*
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* This implementation uses a 256-way trie.
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* The add , contains , delete , and
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* longest prefix methods take time proportional to the length
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* of the key (in the worst case). Construction takes constant time.
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*
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* For additional documentation, see
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* <a href="http://algs4.cs.princeton.edu/52trie">Section 5.2</a> of
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* Algorithms in Java, 4th Edition by Robert Sedgewick and Kevin Wayne.
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*
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* @author Robert Sedgewick
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* @author Kevin Wayne
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*/
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public class TrieSET implements Iterable<String> {
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private static final int R = 256; // extended ASCII
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private Node root; // root of trie
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private int N; // number of keys in trie
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// R-way trie node
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private static class Node {
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private Node[] next = new Node[R];
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private boolean isString;
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}
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/**
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* Initializes an empty set of strings.
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*/
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public TrieSET() {
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}
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/**
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* Does the set contain the given key?
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* @param key the key
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* @return true if the set contains key and
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* false otherwise
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* @throws NullPointerException if key is null
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*/
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public boolean contains(String key) {
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Node x = get(root, key, 0);
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if (x == null) return false;
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return x.isString;
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}
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private Node get(Node x, String key, int d) {
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if (x == null) return null;
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if (d == key.length()) return x;
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char c = key.charAt(d);
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return get(x.next[c], key, d+1);
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}
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/**
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* Adds the key to the set if it is not already present.
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* @param key the key to add
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* @throws NullPointerException if key is null
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*/
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public void add(String key) {
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root = add(root, key, 0);
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}
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private Node add(Node x, String key, int d) {
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if (x == null) x = new Node();
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if (d == key.length()) {
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if (!x.isString) N++;
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x.isString = true;
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}
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else {
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char c = key.charAt(d);
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x.next[c] = add(x.next[c], key, d+1);
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}
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return x;
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}
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/**
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* Returns the number of strings in the set.
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* @return the number of strings in the set
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*/
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public int size() {
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return N;
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}
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/**
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* Is the set empty?
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* @return true if the set is empty, and false otherwise
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*/
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public boolean isEmpty() {
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return size() == 0;
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}
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/**
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* Returns all of the keys in the set, as an iterator.
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* To iterate over all of the keys in a set named set , use the
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* foreach notation: for (Key key : set) .
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* @return an iterator to all of the keys in the set
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*/
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public Iterator<String> iterator() {
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return keysWithPrefix("").iterator();
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}
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/**
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* Returns all of the keys in the set that start with prefix .
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* @param prefix the prefix
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* @return all of the keys in the set that start with prefix ,
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* as an iterable
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*/
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public Iterable<String> keysWithPrefix(String prefix) {
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Queue<String> results = new Queue<String>();
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Node x = get(root, prefix, 0);
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collect(x, new StringBuilder(prefix), results);
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return results;
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}
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private void collect(Node x, StringBuilder prefix, Queue<String> results) {
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if (x == null) return;
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if (x.isString) results.enqueue(prefix.toString());
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for (char c = 0; c < R; c++) {
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prefix.append(c);
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collect(x.next[c], prefix, results);
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prefix.deleteCharAt(prefix.length() - 1);
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}
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}
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/**
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* Returns all of the keys in the set that match pattern ,
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* where . symbol is treated as a wildcard character.
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* @param pattern the pattern
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* @return all of the keys in the set that match pattern ,
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* as an iterable, where . is treated as a wildcard character.
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*/
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public Iterable<String> keysThatMatch(String pattern) {
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Queue<String> results = new Queue<String>();
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StringBuilder prefix = new StringBuilder();
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collect(root, prefix, pattern, results);
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return results;
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}
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private void collect(Node x, StringBuilder prefix, String pattern, Queue<String> results) {
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if (x == null) return;
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int d = prefix.length();
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if (d == pattern.length() && x.isString)
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results.enqueue(prefix.toString());
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if (d == pattern.length())
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return;
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char c = pattern.charAt(d);
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if (c == '.') {
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for (char ch = 0; ch < R; ch++) {
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prefix.append(ch);
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collect(x.next[ch], prefix, pattern, results);
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prefix.deleteCharAt(prefix.length() - 1);
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}
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}
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else {
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prefix.append(c);
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collect(x.next[c], prefix, pattern, results);
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prefix.deleteCharAt(prefix.length() - 1);
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}
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}
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/**
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* Returns the string in the set that is the longest prefix of query ,
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* or null , if no such string.
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* @param query the query string
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* @throws NullPointerException if query is null
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* @return the string in the set that is the longest prefix of query ,
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* or null if no such string
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*/
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public String longestPrefixOf(String query) {
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int length = longestPrefixOf(root, query, 0, -1);
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if (length == -1) return null;
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return query.substring(0, length);
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}
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// returns the length of the longest string key in the subtrie
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// rooted at x that is a prefix of the query string,
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// assuming the first d character match and we have already
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// found a prefix match of length length
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private int longestPrefixOf(Node x, String query, int d, int length) {
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if (x == null) return length;
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if (x.isString) length = d;
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if (d == query.length()) return length;
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char c = query.charAt(d);
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return longestPrefixOf(x.next[c], query, d+1, length);
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}
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/**
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* Removes the key from the set if the key is present.
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* @param key the key
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* @throws NullPointerException if key is null
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*/
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public void delete(String key) {
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root = delete(root, key, 0);
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}
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private Node delete(Node x, String key, int d) {
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if (x == null) return null;
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if (d == key.length()) {
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if (x.isString) N--;
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x.isString = false;
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}
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else {
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char c = key.charAt(d);
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x.next[c] = delete(x.next[c], key, d+1);
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}
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// remove subtrie rooted at x if it is completely empty
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if (x.isString) return x;
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for (int c = 0; c < R; c++)
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if (x.next[c] != null)
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return x;
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return null;
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}
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/**
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* Unit tests the TrieSET data type.
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*/
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public static void main(String[] args) {
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TrieSET set = new TrieSET();
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while (!StdIn.isEmpty()) {
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String key = StdIn.readString();
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set.add(key);
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}
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// print results
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if (set.size() < 100) {
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StdOut.println("keys(\"\"):");
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for (String key : set) {
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StdOut.println(key);
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}
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StdOut.println();
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}
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StdOut.println("longestPrefixOf(\"shellsort\"):");
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StdOut.println(set.longestPrefixOf("shellsort"));
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StdOut.println();
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StdOut.println("longestPrefixOf(\"xshellsort\"):");
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StdOut.println(set.longestPrefixOf("xshellsort"));
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StdOut.println();
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StdOut.println("keysWithPrefix(\"shor\"):");
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for (String s : set.keysWithPrefix("shor"))
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StdOut.println(s);
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StdOut.println();
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StdOut.println("keysWithPrefix(\"shortening\"):");
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for (String s : set.keysWithPrefix("shortening"))
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StdOut.println(s);
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StdOut.println();
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StdOut.println("keysThatMatch(\".he.l.\"):");
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for (String s : set.keysThatMatch(".he.l."))
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StdOut.println(s);
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}
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}
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