Lecture 169:-K Queues In An Array

Implementing multiple queues in a single array is a useful data structure problem. It involves partitioning the array into segments, each representing a separate queue. The challenge is to manage the enqueue and dequeue operations for each queue while efficiently utilizing the available space. One common approach is to use an array to store the elements and additional data structures to track the front and rear of each queue.

Here's a basic implementation of K queues in an array using Python:

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class KQueuesInArray: def __init__(self, k, size): self.k = k # Number of queues self.size = size # Total size of the array self.queue_data = [None] * self.size # Array to store elements self.front = [-1] * self.k # Array to track fronts of queues self.rear = [-1] * self.k # Array to track rears of queues self.next_available = 0 # Next available index in the array self.next_index = list(range(1, self.size)) + [-1] # Array to track available indices def is_full(self): return self.next_available == -1 def is_empty(self, q): return self.front[q] == -1 def enqueue(self, q, item): if self.is_full(): print("Queue is full") return new_index = self.next_available self.next_available = self.next_index[new_index] if self.is_empty(q): self.front[q] = new_index else: self.next_index[self.rear[q]] = new_index self.next_index[new_index] = -1 self.rear[q] = new_index self.queue_data[new_index] = item def dequeue(self, q): if self.is_empty(q): print(f"Queue {q} is empty") return None front_index = self.front[q] item = self.queue_data[front_index] self.front[q] = self.next_index[front_index] self.next_index[front_index] = self.next_available self.next_available = front_index return item

In this implementation, KQueuesInArray is a class that initializes K queues in a single array. It uses three arrays: queue_data to store elements, front to track the front index of each queue, and rear to track the rear index of each queue. The next_index array helps manage available indices in the array. The next_available index indicates the next free position in the array.

The enqueue method adds an element to the specified queue, and the dequeue method removes and returns an element from the specified queue.

Please note that this is a basic implementation, and there are more advanced techniques to optimize space usage and improve performance. For example, circular arrays or dynamic resizing could be employed to make the implementation more efficient.