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