From 31264253a01213fbefd8c5a0a3dc52914107ef5e Mon Sep 17 00:00:00 2001
From: Santo Cariotti <santo@dcariotti.me>
Date: Mon, 16 Jan 2023 20:58:14 +0100
Subject: Add reverse-heapsort

---
 Year_2/Algorithms/reverse-heapsort.cc | 186 ++++++++++++++++++++++++++++++++++
 1 file changed, 186 insertions(+)
 create mode 100644 Year_2/Algorithms/reverse-heapsort.cc

diff --git a/Year_2/Algorithms/reverse-heapsort.cc b/Year_2/Algorithms/reverse-heapsort.cc
new file mode 100644
index 0000000..016ce10
--- /dev/null
+++ b/Year_2/Algorithms/reverse-heapsort.cc
@@ -0,0 +1,186 @@
+#include <fstream>
+#include <iostream>
+#include <string>
+
+using namespace std;
+
+enum class HeapType {
+    Min,
+    Max
+};
+
+template <typename H>
+class Heap {
+public:
+    Heap(HeapType type, int n)
+        : n_ { n + 1 }
+        , type_ { type }
+    {
+        a_ = new H[n + 1];
+        a_[0] = 0;
+    }
+
+    ~Heap()
+    {
+        delete[] a_;
+    }
+
+    void
+    heapify(int i)
+    {
+        if (heapsize_ >= 1)
+            count_++;
+
+        int l = left(i);
+        int r = right(i);
+        int max = i;
+
+        if (l <= heapsize_ && compare(l, max))
+            max = l;
+        if (r <= heapsize_ && compare(r, max))
+            max = r;
+
+        if (max != i) {
+            swap(a_[i], a_[max]);
+            heapify(max);
+        }
+    }
+
+    void
+    build(H aux[], int n)
+    {
+        a_ = aux;
+        heapsize_ = n;
+
+        for (int i = heapsize_ / 2; i > 0; --i) {
+            heapify(i);
+        }
+    }
+
+    H
+    extract()
+    {
+        swap(a_[1], a_[heapsize_]);
+        heapsize_--;
+        heapify(1);
+
+        return a_[heapsize_ + 1];
+    }
+
+    inline int
+    left(int i)
+    {
+        return i << 1;
+    }
+    inline int
+    right(int i)
+    {
+        return (i << 1) | 1;
+    }
+
+    void
+    sort(ostream& out)
+    {
+        H* b = new H[heapsize_ + 1];
+
+        int n = heapsize_;
+
+        for (unsigned i = n; i > 0; --i) {
+            b[i] = extract();
+        }
+        out << count_ << ' ';
+        for (unsigned i = 1; i < n_; ++i) {
+            out << b[i] << ' ';
+        }
+        out << endl;
+
+        delete[] b;
+    }
+
+private:
+    H* a_;
+    int heapsize_ { 0 };
+    int n_;
+    HeapType type_;
+
+    bool
+    compare(int i, int j)
+    {
+        return (type_ == HeapType::Max) ? a_[i] > a_[j] : a_[j] > a_[i];
+    }
+    int count_ { 0 };
+};
+
+int
+main(int argc, char** argv)
+{
+    int n = (argc > 1) ? stoi(argv[1]) : 100;
+    ifstream fin("input.txt");
+    ofstream fout("output.txt");
+
+    string t;
+    int m;
+
+    for (int i = 0; i < n; ++i) {
+        fin >> t >> m;
+
+        if (t == "int") {
+            Heap<int>* pq = new Heap<int>(HeapType::Min, m);
+            int* k = new int[m + 1];
+
+            k[0] = 0;
+            for (int j = 1; j <= m; ++j) {
+                fin >> k[j];
+            }
+            pq->build(k, m);
+
+            pq->sort(fout);
+
+            delete pq;
+        } else if (t == "double") {
+            Heap<double>* pq = new Heap<double>(HeapType::Min, m);
+            double* k = new double[m + 1];
+
+            k[0] = 0;
+            for (int j = 1; j <= m; ++j) {
+                fin >> k[j];
+            }
+            pq->build(k, m);
+
+            pq->sort(fout);
+
+            delete pq;
+        } else if (t == "bool") {
+            Heap<bool>* pq = new Heap<bool>(HeapType::Min, m);
+            bool* k = new bool[m + 1];
+
+            k[0] = 0;
+            for (int j = 1; j <= m; ++j) {
+                fin >> k[j];
+            }
+            pq->build(k, m);
+
+            pq->sort(fout);
+
+            delete pq;
+        } else if (t == "char") {
+            Heap<char>* pq = new Heap<char>(HeapType::Min, m);
+            char* k = new char[m + 1];
+
+            k[0] = 0;
+            for (int j = 1; j <= m; ++j) {
+                fin >> k[j];
+            }
+            pq->build(k, m);
+
+            pq->sort(fout);
+
+            delete pq;
+        }
+    }
+
+    fin.close();
+    fout.close();
+
+    return 0;
+}
-- 
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