[Algorithm] 우선순위 큐(Priority Queues)_TIL Day3-3

우선순위 큐(Priority Queues)

 

특징

- 큐가 FIFO 방식을 따르지 않고 원소들의 우선순위에 따라 큐에서 빠져나오는 방식

- 대표적으로 운영체제의 CPU 스케줄러가 있음

- Enqueue(큐 삽입) 할 때 우선순위 순서를 유지하도록 하는것이 Dequeue보다 유리함

- 연결 리스트를 활용하는것이 더 유리함 (중간에 데이터를 삽입하는일이 빈번함)

 

양방향 연결 리스트를 이용해 우선순위 큐 구현해보기

class Node:

    def __init__(self, item):
        self.data = item
        self.prev = None
        self.next = None


class DoublyLinkedList:

    def __init__(self):
        self.nodeCount = 0
        self.head = Node(None)
        self.tail = Node(None)
        self.head.prev = None
        self.head.next = self.tail
        self.tail.prev = self.head
        self.tail.next = None


    def __repr__(self):
        if self.nodeCount == 0:
            return 'LinkedList: empty'

        s = ''
        curr = self.head
        while curr.next.next:
            curr = curr.next
            s += repr(curr.data)
            if curr.next.next is not None:
                s += ' -> '
        return s


    def getLength(self):
        return self.nodeCount


    def traverse(self):
        result = []
        curr = self.head
        while curr.next.next:
            curr = curr.next
            result.append(curr.data)
        return result


    def reverse(self):
        result = []
        curr = self.tail
        while curr.prev.prev:
            curr = curr.prev
            result.append(curr.data)
        return result


    def getAt(self, pos):
        if pos < 0 or pos > self.nodeCount:
            return None

        if pos > self.nodeCount // 2:
            i = 0
            curr = self.tail
            while i < self.nodeCount - pos + 1:
                curr = curr.prev
                i += 1
        else:
            i = 0
            curr = self.head
            while i < pos:
                curr = curr.next
                i += 1

        return curr


    def insertAfter(self, prev, newNode):
        next = prev.next
        newNode.prev = prev
        newNode.next = next
        prev.next = newNode
        next.prev = newNode
        self.nodeCount += 1
        return True


    def insertAt(self, pos, newNode):
        if pos < 1 or pos > self.nodeCount + 1:
            return False

        prev = self.getAt(pos - 1)
        return self.insertAfter(prev, newNode)


    def popAfter(self, prev):
        curr = prev.next
        next = curr.next
        prev.next = next
        next.prev = prev
        self.nodeCount -= 1
        return curr.data


    def popAt(self, pos):
        if pos < 1 or pos > self.nodeCount:
            return None

        prev = self.getAt(pos - 1)
        return self.popAfter(prev)


    def concat(self, L):
        self.tail.prev.next = L.head.next
        L.head.next.prev = self.tail.prev
        self.tail = L.tail

        self.nodeCount += L.nodeCount


class PriorityQueue:

    def __init__(self):
        self.queue = DoublyLinkedList()


    def size(self):
        return self.queue.getLength()

    def isEmpty(self):
        return self.size() == 0

    def enqueue(self, x):
        newNode = Node(x)
        curr = self.queue.head

        while curr.next.data != None and newNode.data < curr.next.data:
            curr = curr.next
            
        self.queue.insertAfter(curr, newNode)

    def dequeue(self):
        return self.queue.popAt(self.queue.getLength())

    def peek(self):
        return self.queue.getAt(self.queue.getLength()).data


def solution(x):
    return 0