From ee9cd968fb929ba259f0e32024368be29242938e Mon Sep 17 00:00:00 2001
From: Stoycho Kyosev <stoycho.kk@gmail.com>
Date: Tue, 10 Dec 2024 17:05:34 -0500
Subject: Add Sem09

---
 Seminar09/src/priority-queue/heapsort.cpp       |  80 ++++++++++++++
 Seminar09/src/priority-queue/priority-queue.hpp | 133 ++++++++++++++++++++++++
 2 files changed, 213 insertions(+)
 create mode 100644 Seminar09/src/priority-queue/heapsort.cpp
 create mode 100644 Seminar09/src/priority-queue/priority-queue.hpp

(limited to 'Seminar09/src/priority-queue')

diff --git a/Seminar09/src/priority-queue/heapsort.cpp b/Seminar09/src/priority-queue/heapsort.cpp
new file mode 100644
index 0000000..28e499a
--- /dev/null
+++ b/Seminar09/src/priority-queue/heapsort.cpp
@@ -0,0 +1,80 @@
+#include <iostream>
+#include <vector>
+
+void heapify(std::vector<int>& _data, size_t index, size_t array_size)
+{
+    int current_index = index;
+
+    while(true)
+    {
+        size_t left_index = 2 * current_index + 1;
+        size_t right_index = 2 * current_index + 2;
+
+        bool go_left = left_index < array_size && _data[current_index] < _data[left_index];
+        bool go_right = right_index < array_size && _data[current_index] < _data[right_index];
+
+        if(!go_left && !go_right)
+        {
+            break;
+        }
+
+        if(go_left && go_right)
+        {
+            if(_data[left_index] < _data[right_index])
+            {
+                std::swap(_data[current_index], _data[right_index]);
+                current_index = right_index;
+            }
+            else
+            {
+                std::swap(_data[current_index], _data[left_index]);
+                current_index = left_index;
+            }
+        }
+        else if(go_left)
+        {
+            std::swap(_data[current_index], _data[left_index]);
+            current_index = left_index;
+        }
+        else 
+        {
+            std::swap(_data[current_index], _data[right_index]);
+            current_index = right_index;
+        }
+    }
+}
+
+void build_heap(std::vector<int>& data)
+{
+    for(int i = data.size() / 2 - 1; i >= 0; i--)
+        heapify(data, i, data.size());
+}
+
+void heap_sort(std::vector<int>& data)
+{
+    build_heap(data);
+
+    int current_min = data.size() - 1;
+
+    for (size_t i = 0; i < data.size() - 1; i++)
+    {
+        std::swap(data[0], data[current_min--]);
+        heapify(data, 0, current_min);
+    }
+}
+
+int main()
+{
+    std::vector<int> v;
+    for (size_t i = 0; i < 100; i++)
+    {
+        v.push_back(rand() % 100);
+    }
+    
+    heap_sort(v);
+
+    for(int x : v)
+    {
+        std::cout << x << " ";
+    }
+}
\ No newline at end of file
diff --git a/Seminar09/src/priority-queue/priority-queue.hpp b/Seminar09/src/priority-queue/priority-queue.hpp
new file mode 100644
index 0000000..4e54d63
--- /dev/null
+++ b/Seminar09/src/priority-queue/priority-queue.hpp
@@ -0,0 +1,133 @@
+#pragma once
+#include <vector>
+#include <stdexcept>
+
+class priority_queue
+{
+private:
+    static size_t left_child(size_t index);
+    static size_t right_child(size_t index);
+    static int parent(int index);
+
+    void heapify(size_t index);
+public:
+    priority_queue() = default;
+
+    // build_heap
+    priority_queue(const std::vector<int>& data);
+
+    void push(int element);
+    int peek() const;
+    void pop();
+
+    bool empty() const;
+    size_t size() const;
+
+private:
+    std::vector<int> _data;
+};
+
+size_t priority_queue::left_child(size_t index)
+{
+    return 2 * index + 1;
+}
+
+size_t priority_queue::right_child(size_t index)
+{
+    return 2 * index + 2;
+}
+
+int priority_queue::parent(int index)
+{
+    return (index - 1) / 2;
+}
+
+void priority_queue::heapify(size_t index)
+{
+    size_t current_index = index;
+
+    while(true)
+    {
+        size_t left_index = left_child(current_index);
+        size_t right_index = right_child(current_index);
+
+        bool go_left  = left_index < _data.size()  && _data[current_index] < _data[left_index];
+        bool go_right = right_index < _data.size() && _data[current_index] < _data[right_index];
+
+        if(!go_left && !go_right)
+        {
+            break;
+        }
+        
+        if(go_left && go_right)
+        {
+            if(_data[left_index] > _data[right_index])
+            {
+                std::swap(_data[current_index], _data[left_index]);
+                current_index = left_index;
+            }
+            else
+            {
+                std::swap(_data[current_index], _data[right_index]);
+                current_index = right_index;
+            }
+        }
+        else if(go_left)
+        {
+            std::swap(_data[current_index], _data[left_index]);
+            current_index = left_index;
+        }
+        else // go_right
+        {
+            std::swap(_data[current_index], _data[right_index]);
+            current_index = right_index;
+        }
+    }
+}
+
+priority_queue::priority_queue(const std::vector<int>& data) :
+    _data(data)
+{
+    // build_heap
+    for (int i = _data.size() / 2 - 1; i >= 0; i--)
+        heapify(i);    
+}
+
+void priority_queue::push(int element)
+{
+    _data.push_back(element);
+    int index = _data.size() - 1;
+    int parent_index = parent(index);
+
+    while(index > 0 && _data[index] > _data[parent_index])
+    {
+        std::swap(_data[index], _data[parent_index]);
+        index = parent_index;
+        parent_index = parent(index);
+    }
+}
+
+int priority_queue::peek() const
+{
+    return _data[0];
+}
+
+void priority_queue::pop() 
+{
+    if(empty())
+        throw std::runtime_error("Pop on empty queue");
+    
+   _data[0] = _data.back();
+   _data.pop_back();
+   heapify(0); 
+}
+
+size_t priority_queue::size() const
+{
+    return _data.size();
+}
+
+bool priority_queue::empty() const
+{
+    return size() == 0;
+}
\ No newline at end of file
-- 
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