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Queue(큐)

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Queue(큐)란?

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\"Queue(큐)\"\n출처1

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Queue(큐) 구현

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Queue(큐)에는 선형과 환형이 존재한다. 선형 큐의 크기가 제한되어 있고 de_queue 연산시 모든 데이터를 한 칸씩 옮겨야 하는 단점을 보완하여 만들어진 환형 큐이지만, 환형 큐도 큐의 길이를 유동적으로 늘릴 수 없는 단점이 있기에 이 포스트에서는 lineked list(연결 리스트)로 queue(큐)를 구현한다.

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Queue(큐) 구현 시 다음의 메소드들은 꼭 필요하다.

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  1. en_queue(data) = 삽입(push) : data node를 queue에 push(삽입)한다.
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  2. de_queue() = 삭제(pop) : queue(큐)의 front(head) node를 pop(삭제)하고, 가장 앞에 있는 node를 front(head) node로 지정한다.
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추가적으로 queue가 비었는지 차있는지 확인해주는 isempty()메소드와, front(head) & rear(tail) node의 data를 반환해주는 getfront() & get_rear()메소드들과 같이, 상황에 맞게 만들어진 사용자 정의 메소드들이 많이 쓰인다.

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Queue(큐) linked list 구현 코드 (C++)

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#include <iostream>\n\ntemplate <typename T>\nstruct Node {\n\tT data;\n\tstruct Node *front;\n\tstruct Node *rear;\n};\n\ntemplate <typename T>\nclass Queue {\nprivate:\n\tNode<T> *head;\n\tNode<T> *tail;\n\tint size;\n\t\npublic:\n\tQueue() : head(nullptr), tail(nullptr) , size(0) {}\n\t~Queue() {\n\t\tif (this->head == nullptr)\n\t\t\treturn;\n\t\t\n\t\tNode<T> *cur = this->tail;\n\t\t\n\t\twhile (cur != nullptr) {\n\t\t\tcur = cur->front;\n\t\t\tdelete this->tail;\n\t\t\tthis->tail = cur;\n\t\t}\n\t\t\n\t\tthis->head = this->tail;\n\t}\n\t\n\tint get_size() {\n\t\treturn this->size;\n\t}\n\t\n\tbool is_empty() {\n\t\treturn this->head == nullptr ? true : false;\n\t}\n\t\n\tvoid en_queue(T value) {\n\t\tNode<T> *node = new Node<T>;\n\t\tnode->data = value;\n\t\tnode->front = nullptr;\n\t\tnode->rear = nullptr;\n\t\t\n\t\tif (is_empty()) // first push.\n\t\t\tthis->head = node;\n\t\telse {\n\t\t\tnode->front = this->tail;\n\t\t\tthis->tail->rear = node;\n\t\t}\n\t\t\n\t\tthis->tail = node;\n\t\t++size;\n\t}\n\t\n\tT de_queue() {\n\t\tif (is_empty()) // empty queue\n\t\t\treturn -1; // T type에 맞는 error code return.\n\t\telse {\n\t\t\tint pop_val = this->head->data;\n\t\t\t\n\t\t\tif (this->head == this->tail) { // queue with 1 element.\n\t\t\t\tdelete this->head;\n\t\t\t\tthis->head = this->tail = nullptr;\n\t\t\t}\n\t\t\telse { // queue with more than 2 elements.\n\t\t\t\tNode<T> *node = new Node<T>;\n\t\t\t\t\n\t\t\t\tnode = this->head->rear;\n\t\t\t\t\n\t\t\t\tdelete this->head;\n\t\t\t\t\n\t\t\t\tthis->head = node;\n\t\t\t\tthis->head->front = nullptr;\n\t\t\t}\n\t\t\t\n\t\t\t--size;\n\t\t\treturn pop_val;\n\t\t}\n\t}\n\t\n\tT get_head() {\n\t\tif (is_empty()) // empty queue\n\t\t\treturn -1; // T type에 맞는 error code return.\n\t\telse\n\t\t\treturn this->head->data;\n\t}\n\t\n\tT get_tail() {\n\t\tif (is_empty()) // empty queue\n\t\t\treturn -1; // T type에 맞는 error code return.\n\t\telse\n\t\t\treturn this->tail->data;\n\t}\n\t\n\tfriend std::ostream& operator <<(std::ostream &out, Queue<T> &queue){\n\t\tNode<T> *temp = queue.head;\n\t\t\n\t\tfor (int i = 0; i < queue.get_size(); ++i)\n\t\t\tout << \"──\";\n\t\tstd::cout << std::endl;\n\t\t\n\t\twhile(temp != nullptr) {\n\t\t\tout << temp->data << \" \";\n\t\t\ttemp = temp->rear;\n\t\t}\n\t\tstd::cout << std::endl;\n\t\t\n\t\tfor (int i = 0; i < queue.get_size(); ++i)\n\t\t\tout << \"──\";\n\t\tstd::cout << std::endl;\n\t\t\n\t\treturn out;\n\t}\t\n};\nint main() {\n\tstd::ios::sync_with_stdio(false);\n\tstd::cin.tie(NULL); \n\tstd::cout.tie(NULL);\n\t\n\tQueue<int> queue;\n\t\n\tstd::cout << \"Queue en_queue(push) : \" << 1 << std::endl;\n\tqueue.en_queue(1);\n\tstd::cout << queue;\n\t\n\tstd::cout << \"Queue en_queue(push) : \" << 2 << std::endl;\n\tqueue.en_queue(2);\n\tstd::cout << queue;\n\t\n\tstd::cout << \"Queue en_queue(push) : \" << 4 << std::endl;\n\tqueue.en_queue(4);\n\tstd::cout << queue;\n\t\n\tstd::cout << \"Queue length(size) : \" << queue.get_size() << std::endl;\n\tstd::cout << \"Queue front(head) : \" << queue.get_head() << std::endl;\n\tstd::cout << \"Queue rear(tail) : \" << queue.get_tail() << std::endl;\n\t\n\t\n\tstd::cout << \"Queue de_queue(pop) : \" << queue.de_queue() << std::endl;\n\tstd::cout << queue;\n\t\n\tstd::cout << \"Queue de_queue(pop) : \" << queue.de_queue() << std::endl;\n\tstd::cout << queue;\n\t\n\tstd::cout << \"Queue de_queue(pop) : \" << queue.de_queue() << std::endl;\n\tstd::cout << queue;\n\t\n\tstd::cout << \"Queue de_queue(pop) : \" << queue.de_queue() << std::endl;\n\tstd::cout << queue;\n\t\n\treturn 0;\n}
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References

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https://ko.wikipedia.org/wiki/%ED%81%90(%EC%9E%90%EB%A3%8C%EA%B5%AC%EC%A1%B0)
\nhttps://gmlwjd9405.github.io/2018/08/02/data-structure-queue.html
\nhttps://galid1.tistory.com/483

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    https://medium.com/@1991dharapatel/javascript-stacks-and-queues-136fabab8359

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