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123 lines
3.5 KiB
C++
123 lines
3.5 KiB
C++
#pragma once
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#include <algorithm>
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#include <memory>
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#include <utility>
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#include <vector>
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///
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/// \brief A Trie datastructure used to remove prefixes in a set of words.
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/// Insert-only. Iteration over the structure only uses longest matches.
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///
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/// Tests : 1M words, avg words length 4 (geometric dist.), alphabet 50 symbols
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/// trie reduction 58% in 0.4s
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/// set reduction 49% in 1.1s
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///
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/// I did not implement any iterators, as those are quite hard to get right.
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/// There are, however, "internal iterators" exposed as a for_each() member
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/// function (if only we had coroutines already...)
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///
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/// TODO: implement `bool member(...)`
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///
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template <typename T> struct trie {
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/// \brief Inserts a word (given by iterators \p begin and \p end)
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/// \returns true if the element was inserted, false if already there
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template <typename Iterator> bool insert(Iterator && begin, Iterator && end) {
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if (!node) {
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node.reset(new trie_node());
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if (begin == end) {
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return true;
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}
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}
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return node->insert(begin, end);
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}
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/// \brief Inserts a word given as range \p r
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/// \returns true if the element was inserted, false if already there
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template <typename Range> bool insert(Range const & r) { return insert(begin(r), end(r)); }
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/// \brief Applies \p function to all word (not to the prefixes)
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template <typename Fun> void for_each(Fun && function) const {
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if (node) {
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node->for_each(std::forward<Fun>(function));
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} else {
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// empty set, so we don't call the function
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}
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}
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/// \brief Empties the complete set
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void clear() { node.reset(nullptr); }
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private:
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struct trie_node;
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std::unique_ptr<trie_node> node = nullptr;
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// A node always contains the empty word
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struct trie_node {
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template <typename Iterator> bool insert(Iterator && begin, Iterator && end) {
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if (begin == end) return false;
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T i = *begin++;
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auto it = find(i);
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if (it != data.end() && it->first == i) {
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return it->second.insert(begin, end);
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}
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// else, does not yet exist
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it = data.emplace(it, i, trie_node());
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it->second.insert(begin, end);
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return true;
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}
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template <typename Fun> void for_each(Fun && function) const {
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std::vector<T> word;
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return for_each_impl(std::forward<Fun>(function), word);
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}
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private:
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template <typename Fun> void for_each_impl(Fun && function, std::vector<T> & word) const {
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if (data.empty()) {
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// we don't want function to modify word
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const auto & cword = word;
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function(cword);
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}
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for (auto const & kv : data) {
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// for each letter, we extend the word, recurse and remove extension.
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word.push_back(kv.first);
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kv.second.for_each_impl(function, word);
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word.resize(word.size() - 1);
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}
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}
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typename std::vector<std::pair<T, trie_node>>::iterator find(T const & key) {
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return std::lower_bound(
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data.begin(), data.end(), key,
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[](std::pair<T, trie_node> const & kv, T const & k) { return kv.first < k; });
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}
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std::vector<std::pair<T, trie_node>> data;
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};
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};
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/// \brief Flattens a trie \p t
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/// \returns an array of words (without the prefixes)
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template <typename T> std::vector<std::vector<T>> flatten(trie<T> const & t) {
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std::vector<std::vector<T>> ret;
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t.for_each([&ret](std::vector<T> const & w) { ret.push_back(w); });
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return ret;
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}
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/// \brief Returns size and total sum of symbols
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template <typename T> std::pair<size_t, size_t> total_size(trie<T> const & t) {
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size_t count = 0;
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size_t total_count = 0;
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t.for_each([&count, &total_count](std::vector<T> const & w) {
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++count;
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total_count += w.size();
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});
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return {count, total_count};
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}
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