Repo created

libs/indexer/string_set.hpp

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+#pragma once
+
+#include "base/buffer_vector.hpp"
+#include "base/macros.hpp"
+
+#include <cstdint>
+#include <memory>
+#include <utility>
+
+namespace search
+{
+// A trie.  TChar is a type of string characters, OutDegree is an
+// expected branching factor. Therefore, both Add(s) and Has(s) have
+// expected complexity O(OutDegree * Length(s)).  For small values of
+// OutDegree this is quite fast, but if OutDegree can be large and you
+// need guaranteed O(Log(AlphabetSize) * Length(s)), refactor this
+// class.
+//
+// TODO (@y): unify this with base::MemTrie.
+template <typename TChar, size_t OutDegree>
+class StringSet
+{
+public:
+  enum class Status
+  {
+    Absent,
+    Prefix,
+    Full,
+  };
+
+  StringSet() = default;
+
+  template <typename TIt>
+  void Add(TIt begin, TIt end)
+  {
+    auto & cur = m_root.MakeMove(begin, end);
+    cur.m_isLeaf = true;
+  }
+
+  template <typename TIt>
+  Status Has(TIt begin, TIt end) const
+  {
+    auto const * cur = m_root.Move(begin, end);
+    if (!cur)
+      return Status::Absent;
+
+    return cur->m_isLeaf ? Status::Full : Status::Prefix;
+  }
+
+private:
+  struct Node
+  {
+    Node() : m_isLeaf(false) {}
+
+    // Tries to move from the current node by |c|. If the move can't
+    // be made, returns nullptr.
+    Node const * Move(TChar c) const
+    {
+      for (auto const & p : m_moves)
+        if (p.first == c)
+          return p.second.get();
+      return nullptr;
+    }
+
+    // Tries to move from the current node by [|begin|, |end|). If the
+    // move can't be made, returns nullptr.
+    template <typename TIt>
+    Node const * Move(TIt begin, TIt end) const
+    {
+      Node const * cur = this;
+      for (; begin != end && cur; ++begin)
+        cur = cur->Move(*begin);
+      return cur;
+    }
+
+    // Moves from the current node by |c|. If the move can't be made,
+    // creates a new sub-tree and moves to it.
+    Node & MakeMove(TChar c)
+    {
+      for (auto const & p : m_moves)
+        if (p.first == c)
+          return *p.second;
+      m_moves.emplace_back(c, std::make_unique<Node>());
+      return *m_moves.back().second;
+    }
+
+    // Moves from the current node by [|begin|, |end|). If there were
+    // no path from the current node labeled by [|begin|, |end|), this
+    // method will create it.
+    template <typename TIt>
+    Node & MakeMove(TIt begin, TIt end)
+    {
+      Node * cur = this;
+      for (; begin != end; ++begin)
+        cur = &cur->MakeMove(*begin);
+      return *cur;
+    }
+
+    buffer_vector<std::pair<TChar, std::unique_ptr<Node>>, OutDegree> m_moves;
+    bool m_isLeaf;
+
+    DISALLOW_COPY(Node);
+  };
+
+  Node m_root;
+
+  DISALLOW_COPY(StringSet);
+};
+}  // namespace search