update queue.py

changed implementation to not use built in python lists. added english comments

Author: MrWeast

src/python/queue.py

@@ -1,34 +1,90 @@
-""" Implementação da estrutura de dados "fila" """
-
 import random
 
 
+class Node:
+ def __init__(self, value):
+ self.value = value
+ self.left_ptr = None
+
+ @property
+ def prev(self):
+ return self.left_ptr
+
+ @prev.setter
+ def prev(self, ptr):
+ self.left_ptr = ptr
+
+ @property
+ def get_value(self):
+ return self.value
+
+
 class Queue:
  def __init__(self):
- self.__queue = []
+ self.head = None
+ self.tail = None
+ self.length = 0
 
  def enqueue(self, value):
- self.__queue.append(value)
+ new = Node(value)
+ self.length += 1
+ # if empty make new node both head and tail of queue
+ if self.head is None:
+ self.head = new
+ self.tail = new
+ # otherwise add new node to end of queue and update tail
+ else:
+ self.tail.prev = new
+ self.tail = new
 
  def dequeue(self):
- return self.__queue.pop(0)
+ if self.length == 0:
+ print("Queue is empty, cannot dequeue")
+ return
+ else:
+ self.head = self.head.prev
+ self.length -= 1
 
  def show(self):
- print(f"Queue: {self.__queue}")
+ ptr = self.head
+ val = []
+ while ptr is not None:
+ val.append(ptr.get_value)
+ ptr = ptr.prev
+
+ print(val)
+
+ def length(self):
+ return self.length
 
 
 def main():
  queue = Queue()
 
- for _ in range(0, 10):
- queue.enqueue(random.randint(10, 99))
-
+ print("Queuing 1 and 7")
+ queue.enqueue(1)
  queue.show()
+ print(f"Queue is length {queue.length}")
+ queue.enqueue(7)
+ queue.show()
+ print(f"Queue is length {queue.length}")
 
+ print("Dequeuing twice")
  queue.dequeue()
+ queue.show()
+ print(f"Queue is length {queue.length}")
+ queue.dequeue()
+ queue.show()
+ print(f"Queue is length {queue.length}")
+
+ print("Dequeuing again")
  queue.dequeue()
+ print(f"Queue is length {queue.length}")
 
+ print("Queueing 12")
+ queue.enqueue(12)
  queue.show()
+ print(f"Queue is length {queue.length}")
 
 
 if __name__ == "__main__":