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#include "prefix_tree.hh"
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <map>
#include <memory>
#include <optional>
#include <set>
#include <string>
#include <string_view>
namespace prefix_tree {
namespace {
[[nodiscard]]
inline uint8_t get_u8(std::string_view str, size_t index) {
return static_cast<uint8_t>(str[index] & 0xff);
}
[[nodiscard]]
inline uint16_t get_u16(std::string_view str, size_t index) {
return (static_cast<uint16_t>(get_u8(str, index)) << 8) |
get_u8(str, index + 1);
}
inline void write_u8(std::string& str, uint8_t value) {
str.push_back(static_cast<char>(value));
}
inline void write_u16(std::string& str, uint16_t value) {
write_u8(str, value >> 8);
write_u8(str, value & 0xff);
}
class BuilderImpl : public Builder {
public:
BuilderImpl() = default;
void add(std::string_view str) override { strings_.emplace(str); }
[[nodiscard]]
std::optional<std::string> build() const override {
std::string tree;
std::string strings;
std::set<std::string_view> tmp;
for (auto const& str : strings_)
tmp.emplace(str);
if (!write_tree(tmp, tree, strings))
return std::nullopt;
std::string header;
if (tree.size() > 0xffff)
return std::nullopt;
write_u16(header, tree.size());
return header + tree + strings;
}
private:
bool write_tree(std::set<std::string_view> const& input, std::string& tree,
std::string& strings) const {
std::map<char, std::set<std::string_view>> buckets;
bool match = false;
for (auto& str : input) {
if (str.empty()) {
match = true;
continue;
}
buckets[str.front()].emplace(str.substr(1));
}
write_u8(tree, buckets.size() + (match ? 1 : 0));
if (match) {
write_u8(tree, 0);
write_u16(tree, 0);
write_u16(tree, 0);
}
std::string extra;
for (auto& pair : buckets) {
auto it = pair.second.begin();
auto str = *it;
for (++it; it != pair.second.end(); ++it) {
size_t i = 0;
while (i < str.size() && i < it->size() && str[i] == it->at(i))
++i;
if (i == 0) {
str = "";
break;
}
str = str.substr(0, i);
}
write_u8(tree, 1 + str.size());
if (strings.size() > 0xffff)
return false;
write_u16(tree, strings.size());
strings.push_back(pair.first);
strings.append(str);
if (extra.size() > 0xffff)
return false;
write_u16(tree, extra.size());
if (str.empty()) {
if (!write_tree(pair.second, extra, strings))
return false;
} else {
std::set<std::string_view> tmp;
for (auto& str2 : pair.second) {
tmp.emplace(str2.substr(str.size()));
}
if (!write_tree(tmp, extra, strings))
return false;
}
}
tree.append(extra);
return true;
}
std::set<std::string> strings_;
};
} // namespace
std::optional<size_t> lookup(std::string_view tree, std::string_view str) {
size_t base_str = 2 + get_u16(tree, 0);
size_t node = 2;
std::optional<size_t> match;
std::optional<size_t> earlier_match;
while (node < base_str && !str.empty()) {
auto children = get_u8(tree, node);
if (children == 0) {
// Leaf
return match;
}
size_t child_node = node + 1;
size_t child_end = child_node + (static_cast<size_t>(children) * 5);
for (; child_node < child_end; child_node += 5) {
uint8_t len = get_u8(tree, child_node);
uint16_t offset = get_u16(tree, child_node + 1);
if (str.starts_with(tree.substr(base_str + offset, len))) {
// Match but not a leaf, always first in the list of children
if (len == 0) {
earlier_match = match;
continue;
}
match = match.value_or(0) + len;
str = str.substr(len);
auto jump = get_u16(tree, child_node + 3);
node = child_end + jump;
break;
}
}
if (child_node == child_end)
return earlier_match;
}
if (node == base_str)
return earlier_match;
return match;
}
std::unique_ptr<Builder> builder() { return std::make_unique<BuilderImpl>(); }
} // namespace prefix_tree
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