Repo created

libs/coding/sparse_vector.hpp

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+#pragma once
+
+#include "3party/succinct/rs_bit_vector.hpp"
+
+namespace coding
+{
+
+/// Simple sparse vector for better memory usage.
+template <class Value>
+class SparseVector
+{
+  succinct::rs_bit_vector m_bits;
+  std::vector<Value> m_values;
+
+public:
+  SparseVector() = default;
+
+  bool Empty() const { return GetSize() == 0; }
+  uint64_t GetSize() const { return m_bits.size(); }
+  bool Has(uint64_t i) const { return m_bits[i]; }
+  Value const & Get(uint64_t i) const { return m_values[m_bits.rank(i)]; }
+
+  size_t GetMemorySize() const { return m_values.capacity() * sizeof(Value) + m_bits.size() / 8; }
+
+private:
+  SparseVector(std::vector<Value> && values, succinct::bit_vector_builder & bitsBuilder)
+    : m_bits(&bitsBuilder)
+    , m_values(std::move(values))
+  {}
+
+  template <class T>
+  friend class SparseVectorBuilder;
+};
+
+template <class Value>
+class SparseVectorBuilder
+{
+  succinct::bit_vector_builder m_bitsBuilder;
+  std::vector<Value> m_values;
+
+public:
+  explicit SparseVectorBuilder(size_t reserveSize = 0) { m_bitsBuilder.reserve(reserveSize); }
+
+  void PushEmpty() { m_bitsBuilder.push_back(false); }
+  void PushValue(Value v)
+  {
+    m_bitsBuilder.push_back(true);
+    m_values.emplace_back(std::move(v));
+  }
+
+  SparseVector<Value> Build()
+  {
+    // Shrink memory as a primary goal of this component.
+    if (m_values.capacity() / double(m_values.size()) > 1.4)
+      std::vector<Value>(m_values).swap(m_values);
+
+    return SparseVector<Value>(std::move(m_values), m_bitsBuilder);
+  }
+};
+
+}  // namespace coding