Package edu.princeton.cs.algs4

Class TrieST<Value>

  • public class TrieST<Value>
extends Object
    The TrieST class represents a symbol table of key-value pairs, with string keys and generic values. It supports the usual put, get, contains, delete, size, and is-empty methods. It also provides character-based methods for finding the string in the symbol table that is the longest prefix of a given prefix, finding all strings in the symbol table that start with a given prefix, and finding all strings in the symbol table that match a given pattern. 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. Unlike Map, this class 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 256-way trie. The put, contains, delete, and longest prefix operations take time proportional to the length of the key (in the worst case). Construction takes constant time. The size, and is-empty operations take constant time. Construction takes constant time.

    For additional documentation, see Section 5.2 of Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.

    • Constructor Detail

      • TrieST

        public TrieST()
        Initializes an empty string symbol table.

    • Method Detail

      • get

        public Value get​(String key)
        Returns the value associated with the given key.
        Parameters:
        key - the key
        Returns:
        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
        Throws:
        IllegalArgumentException - if key is null

      • contains

        public boolean contains​(String key)
        Does this symbol table contain the given key?
        Parameters:
        key - the key
        Returns:
        true if this symbol table contains key and false otherwise
        Throws:
        IllegalArgumentException - if key is null

      • put

        public void put​(String key,
                Value val)
        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.
        Parameters:
        key - the key
        val - the value
        Throws:
        IllegalArgumentException - if key is null

      • size

        public int size()
        Returns the number of key-value pairs in this symbol table.
        Returns:
        the number of key-value pairs in this symbol table

      • isEmpty

        public boolean isEmpty()
        Is this symbol table empty?
        Returns:
        true if this symbol table is empty and false otherwise

      • keys

        public Iterable<String> keys()
        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()).
        Returns:
        all keys in the symbol table as an Iterable

      • keysWithPrefix

        public Iterable<String> keysWithPrefix​(String prefix)
        Returns all of the keys in the set that start with prefix.
        Parameters:
        prefix - the prefix
        Returns:
        all of the keys in the set that start with prefix, as an iterable

      • keysThatMatch

        public Iterable<String> keysThatMatch​(String pattern)
        Returns all of the keys in the symbol table that match pattern, where the character '.' is interpreted as a wildcard character.
        Parameters:
        pattern - the pattern
        Returns:
        all of the keys in the symbol table that match pattern, as an iterable, where . is treated as a wildcard character.

      • longestPrefixOf

        public String longestPrefixOf​(String query)
        Returns the string in the symbol table that is the longest prefix of query, or null, if no such string.
        Parameters:
        query - the query string
        Returns:
        the string in the symbol table that is the longest prefix of query, or null if no such string
        Throws:
        IllegalArgumentException - if query is null

      • delete

        public void delete​(String key)
        Removes the key from the set if the key is present.
        Parameters:
        key - the key
        Throws:
        IllegalArgumentException - if key is null

      • main

        public static void main​(String[] args)
        Unit tests the TrieST data type.
        Parameters:
        args - the command-line arguments