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GH-174: Priority Queue (Heap) in C++ (#175)
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‎README.md

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@@ -95,6 +95,12 @@ A data structure is a data organization, management, and storage format that is
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<tr>
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<td>Priority Queue (Heap)</td>
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<td>
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<a href="/concepts/cpp/priority_queue.md"><code>cpp🐀</code></a>
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</td>
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</tr>
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<tr>
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<td colspan="2" align="center"><b>Algorithms</b></td>
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</tr>
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‎concepts/abstract/data-structures/priority_queue.png

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‎concepts/cpp/labs/priority_queue.ipynb

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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Priority Queue \n",
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"\n",
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"A priority queue is a container that provides constant time lookup of the largest (by default) element, at the expense of logarithmic insertion and extraction.\n",
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"\n",
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"Real world examples of priority queues include:\n",
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"\n",
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"- The task queue in an operating system\n",
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"- The call queue in a call center\n",
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"- The list of pending requests at a web server, sorted by their priority\n"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Baisc usage of priority queue\n",
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"\n",
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"C++ has built-in object [`priority_queue`](https://cplusplus.com/reference/queue/priority_queue/) in `queue` library."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"vscode": {
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"languageId": "cpp"
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}
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},
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"outputs": [],
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"source": [
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"#include <queue>\n",
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"#include <vector>\n",
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"#include <iostream>\n",
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"\n",
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"using namespace std;"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 13,
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"metadata": {
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"vscode": {
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"languageId": "cpp"
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}
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"5\n",
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"3\n",
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"1\n"
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]
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}
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],
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"source": [
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"priority_queue<int> pq;\n",
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"\n",
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"pq.push(1);\n",
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"pq.push(5);\n",
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"pq.push(3);\n",
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"\n",
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"while (!pq.empty()) {\n",
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" cout << pq.top() << endl;\n",
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" pq.pop();\n",
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"}"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Min priority queue\n",
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"\n",
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"If you want min priority queue, you can use `greater<int>` as the third argument."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 14,
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"metadata": {
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"vscode": {
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"languageId": "cpp"
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}
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"1\n",
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"3\n",
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"5\n"
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]
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}
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],
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"source": [
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"priority_queue<int, vector<int>, greater<int>> pq;\n",
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"\n",
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"pq.push(1);\n",
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"pq.push(5);\n",
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"pq.push(3);\n",
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"\n",
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"while (!pq.empty()) {\n",
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" cout << pq.top() << endl;\n",
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" pq.pop();\n",
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"}"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Priority queue with custom comparator\n",
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"\n",
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"Custom Comparision with `priority_queue` is a little bit interesting. You can use custom struct as the third argument."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 15,
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"metadata": {
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"vscode": {
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"languageId": "cpp"
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}
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},
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"outputs": [],
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"source": [
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"struct Node {\n",
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" int val;\n",
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" int priority;\n",
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"};\n",
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"\n",
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"struct compare{\n",
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" public:\n",
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" bool operator()(Node& a,Node& b)\n",
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" {\n",
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" return a.priority < b.priority;\n",
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" }\n",
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"};"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 16,
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"metadata": {
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"vscode": {
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"languageId": "cpp"
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}
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},
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"outputs": [],
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"source": [
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"priority_queue<Node, vector<Node>, compare> pq;\n",
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"pq.push({1, 2});\n",
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"pq.push({5, 6});\n",
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"pq.push({10, 3});"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 17,
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"metadata": {
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"vscode": {
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"languageId": "cpp"
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}
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"5, 6\n",
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"10, 3\n",
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"1, 2\n"
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]
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}
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],
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"source": [
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"while(!pq.empty()){\n",
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" Node tmp = pq.top();\n",
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" cout << tmp.val << \", \" << tmp.priority << endl;\n",
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" pq.pop();\n",
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"}"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## References\n",
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"\n",
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"* [Declaring a priority_queue in c++ with a custom comparator](https://stackoverflow.com/questions/16111337/declaring-a-priority-queue-in-c-with-a-custom-comparator)"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "C++17",
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"language": "C++17",
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"name": "xcpp17"
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},
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"language_info": {
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"codemirror_mode": "text/x-c++src",
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"file_extension": ".cpp",
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"mimetype": "text/x-c++src",
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"name": "c++",
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"version": "17"
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},
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"orig_nbformat": 4
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},
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"nbformat": 4,
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"nbformat_minor": 2
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}

‎concepts/cpp/priority_queue.md

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# Priority Queue
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<a href="https://github.com/rain1024/datastructures-algorithms-competitive-programming/blob/main/concepts/cpp/labs/priority_queue.ipynb">
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<img src="https://img.shields.io/badge/🧪-notebook-brightgreen">
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</a>
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A priority queue is an abstract data type that allows the storage of elements with priority. The elements are stored in such a way that the element with the highest priority is always at the front of the queue, and the element with the lowest priority is at the back of the queue.
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![](../abstract/data-structures/priority_queue.png)
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## 🎨 Priority Queue Design
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**Methods**
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| | Definition |
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|----------------|-------------------------------------------------------------|
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| enqueue | Add element to the queue |
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| dequeue | remove the element with the highest priority from the queue |
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## 💻 Priority Queue Implementation in C++
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C++ has built-in object [`priority_queue`](https://cplusplus.com/reference/queue/priority_queue/) in `queue` library.
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```cpp
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#include <iostream>
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#include <queue>
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int main(){
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priority_queue<int> pq;
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pq.push(1);
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pq.push(5);
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pq.push(3);
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while (!pq.empty()) {
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cout << pq.top() << endl;
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pq.pop();
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}
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return 0;
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}
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```
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## 📈 Complexity Analysis of Priority Queue
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| Operation | Complexity |
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|-----------------|---------------------|
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| push | $O(log N)$ |
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| pop | $O(log N)$ |
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| top | $O(1)$ |
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## 🔗 Further Reading
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* [Priority Queue (data structures)](https://en.wikipedia.org/wiki/Priority_queue), wikipedia
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* ▶️ [Priority Queue (1/5) Introduction](https://www.youtube.com/watch?v=wptevk0bshY&ab_channel=WilliamFiset), WilliamFiset, 2017
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* ▶️ [Priority Queue (2/5) Min Heaps and Max Heaps](https://www.youtube.com/watch?v=HCEr35qpawQ&ab_channel=WilliamFiset), WilliamFiset, 2017
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* ▶️ [Priority Queue (3/5) Inserting Elements](https://www.youtube.com/watch?v=QOJ-CmQiXko&list=PLDV1Zeh2NRsB6SWUrDFW2RmDotAfPbeHu&index=16&ab_channel=WilliamFiset), WilliamFiset, 2017
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* ▶️ [Priority Queue (4/5) Removing Elements](https://www.youtube.com/watch?v=eVq8CmoC1x8&list=PLDV1Zeh2NRsB6SWUrDFW2RmDotAfPbeHu&index=17&ab_channel=WilliamFiset), WilliamFiset, 2017
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* ▶️ [Priority Queue (5/5) Code](https://www.youtube.com/watch?v=GLIRnUhknP0&list=PLDV1Zeh2NRsB6SWUrDFW2RmDotAfPbeHu&index=18&ab_channel=WilliamFiset), WilliamFiset, 2017

‎concepts/cpp/tree.md

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}
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```
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## 📈 Complexity Analysis of [Awesome Type]
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## 📈 Complexity Analysis of Tree
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| Operation | Complexity |

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