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__":