diff --git a/data_structures/queue/circular_queue.py b/data_structures/queue/circular_queue.py new file mode 100644 index 000000000..2ba3f891e --- /dev/null +++ b/data_structures/queue/circular_queue.py @@ -0,0 +1,93 @@ +# Implementation of Circular Queue (using Python lists) + +class CircularQueue: + """Circular FIFO queue with a fixed capacity""" + + def __init__(self, n: int): + self.n = n + self.array = [None] * self.n + self.front = 0 # index of the first element + self.rear = 0 + self.size = 0 + + def __len__(self) -> int: + """ + >>> cq = CircularQueue(5) + >>> len(cq) + 0 + >>> cq.enqueue("A") # doctest: +ELLIPSIS + >> len(cq) + 1 + """ + return self.size + + def is_empty(self) -> bool: + """ + >>> cq = CircularQueue(5) + >>> cq.is_empty() + True + >>> cq.enqueue("A").is_empty() + False + """ + return self.size == 0 + + def first(self): + """ + >>> cq = CircularQueue(5) + >>> cq.first() + False + >>> cq.enqueue("A").first() + 'A' + """ + return False if self.is_empty() else self.array[self.front] + + def enqueue(self, data): + """ + This function insert an element in the queue using self.rear value as an index + >>> cq = CircularQueue(5) + >>> cq.enqueue("A") # doctest: +ELLIPSIS + >> (cq.size, cq.first()) + (1, 'A') + >>> cq.enqueue("B") # doctest: +ELLIPSIS + >> (cq.size, cq.first()) + (2, 'A') + """ + if self.size >= self.n: + raise Exception("QUEUE IS FULL") + + self.array[self.rear] = data + self.rear = (self.rear+1)%self.n + self.size += 1 + return self + + def dequeue(self): + """ + This function removes an element from the queue using on self.front value as an + index + >>> cq = CircularQueue(5) + >>> cq.dequeue() + Traceback (most recent call last): + ... + Exception: UNDERFLOW + >>> cq.enqueue("A").enqueue("B").dequeue() + 'A' + >>> (cq.size, cq.first()) + (1, 'B') + >>> cq.dequeue() + 'B' + >>> cq.dequeue() + Traceback (most recent call last): + ... + Exception: UNDERFLOW + """ + if self.size == 0: + raise Exception("UNDERFLOW") + + temp = self.array[self.front] + self.array[self.front] = None + self.front = (self.front + 1)%self.n + self.size -= 1 + return temp