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algo.h

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+#pragma once
+
+#include <deque>
+
+template<class T, class Comp>
+std::deque<T> Merge(const std::deque<T>& half1, const std::deque<T>& half2, const Comp& comparator) {
+    std::deque<T> result;
+    auto it1 = half1.begin();
+    auto it2 = half2.begin();
+
+    while (it1 != half1.end() && it2 != half2.end()) {
+        if (!comparator(*it2, *it1)) {
+            result.push_back(*it1);
+            ++it1;
+        } else {
+            result.push_back(*it2);
+            ++it2;
+        }
+    }
+
+    while (it1 != half1.end()) {
+        result.push_back(*it1);
+        ++it1;
+    }
+
+    while (it2 != half2.end()) {
+        result.push_back(*it2);
+        ++it2;
+    }
+
+    return result;
+}
+
+template<class T, class Comp>
+std::deque<T> MergeSort(const std::deque<T>& src, const Comp& comparator) {
+    if (src.size() <= 1) {
+        return src;
+    }
+
+    const size_t mid = src.size() / 2;
+    const auto mid_it = std::next(src.begin(), mid);
+
+    const auto left = MergeSort(
+        std::deque<T>(src.begin(), mid_it),
+        comparator
+    );
+    const auto right = MergeSort(
+        std::deque<T>(mid_it, src.end()),
+        comparator
+    );
+
+    return Merge(left, right, comparator);
+}