diff --git a/hashmap.h b/hashmap.h
new file mode 100644
index 0000000..ac032b5
--- /dev/null
+++ b/hashmap.h
@@ -0,0 +1,286 @@
+#include <forward_list>
+#include <functional>
+#include <vector>
+#include <stdexcept>
+#include <type_traits>
+#include <utility>
+
+template<class vector_iter, class list_iter>
+class base_hashmap_iterator {
+private:
+    vector_iter cur, end;
+    list_iter biter;
+
+    void push() {
+        while (cur != end && biter == cur->end()) {
+            ++cur;
+            if (cur != end) {
+                biter = cur->begin();
+            }
+        }
+    }
+
+public:
+    base_hashmap_iterator() = default;
+    base_hashmap_iterator(const base_hashmap_iterator &it) = default;
+
+    base_hashmap_iterator(const vector_iter &_cur, const list_iter &_biter, const vector_iter &_end) :
+        cur(_cur), end(_end), biter(_biter) {}
+
+    template<class list_type>
+    base_hashmap_iterator(std::vector<list_type> &buckets, bool back = false) :
+        cur(buckets.begin()), end(buckets.end()), biter(cur->begin()) {
+        
+        if (!back) {
+            push();
+        } else {
+            cur = end = buckets.end();
+            biter = buckets.back().end();
+        }
+    }
+
+    template<class list_type>
+    base_hashmap_iterator(const std::vector<list_type> &buckets, bool back = false) :
+        cur(buckets.begin()), end(buckets.end()), biter(cur->begin()) {
+        
+        if (!back) {
+            push();
+        } else {
+            cur = end = buckets.end();
+            biter = buckets.back().end();
+        }
+    }
+
+    void bucket_advance(size_t l) {
+        cur += l;
+    }
+
+    base_hashmap_iterator& operator++() {
+        ++biter;
+        push();
+        return *this;
+    }
+
+    base_hashmap_iterator operator++(int) {
+        base_hashmap_iterator cp(*this);
+        ++(*this);
+        return cp;
+    }
+
+    base_hashmap_iterator& operator=(const base_hashmap_iterator &iter) {
+        cur = iter.cur;
+        end = iter.end;
+        biter = iter.biter;
+        return *this;
+    }
+
+    typename list_iter::value_type operator*() {
+        return *biter;
+    }
+
+    list_iter operator->() {
+        return biter;
+    }
+
+    bool operator==(const base_hashmap_iterator &it) {
+        return it.cur == cur && it.biter == biter;
+    }
+
+    bool operator!=(const base_hashmap_iterator &it) {
+        return !(*this == it);
+    }
+};
+
+template<class KeyType, class ValueType, class Hash = std::hash<KeyType>>
+class HashMap {
+private:
+    static constexpr size_t sizes[] = {
+    5, 11, 23, 47, 97, 197, 397, 797, 1597, 3203, 6421,
+    12853, 25717, 51437, 102877, 205759, 411527, 823117,
+    1646237, 3292489, 6584983, 13169977, 26339969, 52679969};
+    static constexpr size_t growLoadFactorThreshold = 130, shrintLoadFactorThreshold = 30;
+
+    using stored_type = std::pair<const KeyType, ValueType>;
+    using list_type = std::forward_list<stored_type>;
+    using vector_type = std::vector<list_type>;
+
+    size_t cur_size = 0, cur_capacity = 0;
+    vector_type buckets;
+    Hash hasher;
+
+    void change_size(size_t new_capacity) {
+        if (new_capacity == cur_capacity) {
+            return;
+        }
+        cur_capacity = new_capacity;
+        new_capacity = sizes[cur_capacity];
+        vector_type new_buckets(new_capacity);
+        for (auto &b : buckets) {
+            for (auto &x : b) {
+                new_buckets[hasher(x.first) % new_capacity].push_front(std::move(x));
+            }
+        }
+        buckets.swap(new_buckets);
+    }
+
+    size_t load_factor() const {  // returns cur_size / cur_capacity in percents. i.e. returns load factor in percents
+        return cur_size * 100 / sizes[cur_capacity];
+    }
+
+    bool trySizeUp() {
+        if (load_factor() > growLoadFactorThreshold) {
+            change_size(cur_capacity + 1);
+            return true;
+        }
+        return false;
+    }
+
+    bool trySizeDown() {
+        if (load_factor() < shrintLoadFactorThreshold && cur_capacity > 0) {
+            change_size(cur_capacity - 1);
+            return true;
+        }
+        return false;
+    }
+
+    std::pair<size_t, size_t> base_find(const KeyType &val) const {
+        size_t h = hasher(val) % buckets.size();
+        for (auto it = buckets[h].begin(), cur = 0ull; it != buckets[h].end(); ++it, ++cur) {
+            if (it->first == val) {
+                return std::make_pair(h, (size_t)cur);
+            }
+        }
+        return std::make_pair(buckets.size(), std::distance(buckets.back().begin(), buckets.back().end()));
+    }
+
+public:
+    explicit HashMap(const Hash &Hasher = Hash()) : buckets(sizes[0]), hasher(Hasher) {}
+
+    template<class Iter>
+    HashMap(Iter beg, Iter end, const Hash &Hasher = Hash()) : HashMap(Hasher) {
+        for (Iter it = beg; it != end; ++it) {
+            insert(*it);
+        }
+    }
+
+    HashMap(const std::initializer_list<stored_type> &l, const Hash &Hasher = Hash()) :
+        HashMap(l.begin(), l.end(), Hasher) {}
+
+    HashMap(const std::vector<stored_type> &vals, const Hash &Hasher = Hash()) :
+        HashMap(vals.begin(), vals.end(), Hasher) {}
+
+    using iterator = base_hashmap_iterator<typename vector_type::iterator, typename list_type::iterator>;
+    using const_iterator = base_hashmap_iterator<typename vector_type::const_iterator,
+                                                 typename list_type::const_iterator>;
+
+    size_t size() const {
+        return cur_size;
+    }
+
+    bool empty() const {
+        return cur_size == 0;
+    }
+
+    const Hash& hash_function() const {
+        return hasher;
+    }
+
+    size_t count(const KeyType &key) const {
+        size_t h = hasher(key) % buckets.size();
+        for (auto &[x, y] : buckets[h]) {
+            if (x == key) {
+                return 1;
+            }
+        }
+        return 0;
+    }
+
+    void insert(const stored_type &val) {
+        if (count(val.first))
+            return;
+        buckets[hasher(val.first) % buckets.size()].push_front(val);
+        ++cur_size;
+        trySizeUp();
+    }
+
+    void erase(const KeyType &key) {
+        size_t h = hasher(key) % buckets.size();
+        for (auto it = buckets[h].before_begin(); next(it) != buckets[h].end(); ++it) {
+            if (next(it)->first == key) {
+                buckets[h].erase_after(it);
+                --cur_size;
+                break;
+            }
+        }
+        trySizeDown();
+    }
+
+    ValueType& operator[](const KeyType &key) {
+        size_t h = hasher(key) % sizes[cur_capacity];
+        for (auto &[x, y] : buckets[h]) {
+            if (x == key) {
+                return y;
+            }
+        }
+        buckets[h].emplace_front(key, ValueType());
+        ++cur_size;
+        if (trySizeUp()) {
+            return operator[](key);
+        }
+        return buckets[h].front().second;
+    }
+
+    const ValueType& at(const KeyType &key) const {
+        size_t h = hasher(key) % buckets.size();
+        for (auto &[x, y] : buckets[h]) {
+            if (x == key) {
+                return y;
+            }
+        }
+        throw std::out_of_range("No such key");
+    }
+
+    void clear() {
+        for (auto &bucket : buckets) {
+            bucket.clear();
+        }
+        cur_size = 0;
+        change_size(0);
+    }
+
+    const_iterator find(const KeyType &val) const {
+        auto [block_idx, item_idx] = base_find(val);
+        auto item_iterator = buckets[std::min(block_idx, buckets.size() - 1)].begin();  // For case of end iterator
+        std::advance(item_iterator, item_idx);
+        return const_iterator(buckets.begin() + block_idx,
+                              item_iterator, buckets.end());
+    }
+
+    iterator find(const KeyType &val) {
+        auto [block_idx, item_idx] = base_find(val);
+        auto item_iterator = buckets[std::min(block_idx, buckets.size() - 1)].begin();
+        std::advance(item_iterator, item_idx);
+        return iterator(buckets.begin() + block_idx,
+                        item_iterator, buckets.end());
+    }
+
+     iterator begin() {
+        iterator iter(buckets);
+        return iter;
+     }
+
+     iterator end() {
+        iterator iter(buckets, true);
+        return iter;
+     }
+
+     const_iterator begin() const {
+        const_iterator iter(buckets);
+        return iter;
+     }
+
+     const_iterator end() const {
+        const_iterator iter(buckets, true);
+        return iter;
+     }
+};