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TrieST.h
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#ifndef CH5_TRIEST_H
#define CH5_TRIEST_H
#include <vector>
#include <string>
#include <queue>
#include <stdexcept>
#include <numeric>
#include <limits>
using std::queue;
using std::vector;
using std::string;
using std::to_string;
using std::invalid_argument;
using std::runtime_error;
using std::numeric_limits;
/**
* The {@code TrieST} class represents an symbol table of key-value
* pairs, with string keys and generic values.
* It supports the usual <em>put</em>, <em>get</em>, <em>contains</em>,
* <em>delete</em>, <em>size</em>, and <em>is-empty</em> methods.
* It also provides character-based methods for finding the string
* in the symbol table that is the <em>longest prefix</em> of a given prefix,
* finding all strings in the symbol table that <em>start with</em> a given prefix,
* and finding all strings in the symbol table that <em>match</em> a given pattern.
* A symbol table implements the <em>associative array</em> 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 {@link java.util.Map}, this class uses the convention that
* values cannot be {@code null}—setting the
* value associated with a key to {@code null} is equivalent to deleting the key
* from the symbol table.
* <p>
* This implementation uses a 256-way trie.
* The <em>put</em>, <em>contains</em>, <em>delete</em>, and
* <em>longest prefix</em> operations take time proportional to the length
* of the key (in the worst case). Construction takes constant time.
* The <em>size</em>, and <em>is-empty</em> operations take constant time.
* Construction takes constant time.
* <p>
* For additional documentation, see <a href="https://algs4.cs.princeton.edu/52trie">Section 5.2</a> of
* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
*/
template<typename Value>
class TrieST {
private:
class Node {
public:
Node() : next(256, nullptr), flag(false), val(0) {}
~Node() {
for (int i = 0; i < R; ++i)
if (next[i]) delete (next[i]);
}
Value val;
bool flag;
vector<Node *> next;
};
public:
TrieST() : n(0), root(nullptr) {}
~TrieST() { delete (root); }
/**
* 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 {@code null} if the key is not in the symbol table
* @throws IllegalArgumentException if {@code key} is {@code null}
*/
Value get(string key) {
if (key.empty()) throw invalid_argument("argument to get() is null");
Node *x = get(root, key, 0);
if (x == nullptr) throw runtime_error("without this key");
return x->val;
}
/**
* Does this symbol table contain the given key?
* @param key the key
* @return {@code true} if this symbol table contains {@code key} and
* {@code false} otherwise
* @throws IllegalArgumentException if {@code key} is {@code null}
*/
bool contains(string key) {
if (key.empty()) throw invalid_argument("argument to contains() is null");
return get(key) != nullptr;
}
/**
* 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 {@code null}, this effectively deletes the key from the symbol table.
* @param key the key
* @param val the value
* @throws IllegalArgumentException if {@code key} is {@code null}
*/
void put(string key, Value val) {
if (key.empty()) throw invalid_argument("first argument to put() is null");
else root = put(this->root, key, val, 0);
}
/**
* Returns the number of key-value pairs in this symbol table.
* @return the number of key-value pairs in this symbol table
*/
int size() {
return n;
}
/**
* Is this symbol table empty?
* @return {@code true} if this symbol table is empty and {@code false} otherwise
*/
bool isEmpty() {
return size() == 0;
}
/**
* Returns all keys in the 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 the symbol table as an {@code Iterable}
*/
queue<string> keys() {
return keysWithPrefix("");
}
/**
* 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
*/
queue<string> keysWithPrefix(string prefix) {
queue<string> results;
Node *x = get(root, prefix, 0);
collect(x, prefix, results);
return results;
}
/**
* Returns all of the keys in the symbol table that match {@code pattern},
* where . symbol is treated as a wildcard character.
* @param pattern the pattern
* @return all of the keys in the symbol table that match {@code pattern},
* as an iterable, where . is treated as a wildcard character.
*/
queue<string> keysThatMatch(string pattern) {
queue<string> results;
collect(root, "", pattern, results);
return results;
}
/**
* Returns the string in the symbol table 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 symbol table that is the longest prefix of {@code query},
* or {@code null} if no such string
* @throws IllegalArgumentException if {@code query} is {@code null}
*/
string longestPrefixOf(string query) {
if (query.empty()) throw invalid_argument("argument to longestPrefixOf() is null");
int length = longestPrefixOf(root, query, 0, -1);
if (length == -1) return "";
else return query.substr(0, length);
}
/**
* Removes the key from the set if the key is present.
* @param key the key
* @throws IllegalArgumentException if {@code key} is {@code null}
*/
void delete_(string key) {
if (key.empty()) throw invalid_argument("argument to delete() is null");
root = delete_(root, key, 0);
}
private:
Node *get(Node *x, string key, int d) {
if (x == nullptr) return nullptr;
if (d == key.length()) return x;
char c = key[d];
return get(x->next[c], key, d + 1);
}
Node *put(Node *x, string key, Value val, int d) {
if (x == nullptr) x = new Node();
if (d == key.length()) {
x->val = val;
x->flag = true;
return x;
}
char c = key[d];
x->next[c] = put(x->next[c], key, val, d + 1);
return x;
}
void collect(Node *x, string prefix, queue<string> &results) {
if (x == nullptr) return;
if (x->flag) results.push(prefix);
for (unsigned char c = 0;; c++) {
prefix.push_back(c);
collect(x->next[c], prefix, results);
prefix.pop_back();
if (c == R - 1) break;
}
}
void collect(Node *x, string prefix, string pattern, queue<string> &results) {
if (x == nullptr) return;
int d = prefix.length();
if (d == pattern.length() && x->flag)
results.push(prefix);
if (d == pattern.length())
return;
char c = pattern[d];
if (c == '.') {
for (unsigned char ch = 0;; ch++) {
prefix.push_back(ch);
collect(x->next[ch], prefix, pattern, results);
prefix.pop_back();
if (ch == R - 1) break;
}
} else {
prefix.push_back(c);
collect(x->next[c], prefix, pattern, results);
prefix.pop_back();
}
}
// 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 given length (-1 if no such match)
int longestPrefixOf(Node *x, string query, int d, int length) {
if (x == nullptr) return length;
if (x->flag) length = d;
if (d == query.length()) return length;
char c = query[d];
return longestPrefixOf(x->next[c], query, d + 1, length);
}
Node *delete_(Node *x, string key, int d) {
if (x == nullptr) return nullptr;
if (d == key.length()) {
if (x->flag) n--;
x->flag = false;
} else {
char c = key[d];
x->next[c] = delete_(x->next[c], key, d + 1);
}
// remove subtrie rooted at x if it is completely empty
if (x->flag) return x;
for (int c = 0; c < R; c++)
if (x->next[c] != nullptr)
return x;
return nullptr;
}
private:
static const int R;
Node *root; // root of trie
int n; // number of keys in trie
};
template<typename Value>
const int TrieST<Value>::R = 256;
#endif //CH5_TRIEST_H