Queue code added

Author: me-shaon

Data Structure/Queue/README.md

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+# Queue
+
+**Queue** is an abstract data structure, somewhat similar to Stacks. Unlike stacks, a queue is open at both its ends. One end is always used to insert data (enqueue) and the other is used to remove data (dequeue). Queue follows First-In-First-Out methodology, i.e., the data item stored first will be accessed first.
+
+A real-world example of queue can be a single-lane one-way road, where the vehicle enters first, exits first. More real-world examples can be seen as queues at the ticket windows and bus-stops.
+
+![Queue](queue.svg)
+
+**Basic Operations:**
+
+Queue operations may involve initializing or defining the queue, utilizing it, and then completely erasing it from the memory.. Apart from these basic stuffs, a queue is used for the following two primary operations −
+
+- **enqueue()** − add (store) an item to the queue.
+- **dequeue()** − remove (access) an item from the queue.
+
+To use a queue efficiently, we need to check the status of queue as well. For the same purpose, the following functionality are available too −
+
+- **peek()** − get the first data element of the queue, without removing it.
+- **isEmpty()** − check if queue is empty.
+
+
+#### Complexity Analysis
+- Insertion - O(1)
+- Deletion - O(1) (If implemented with array, then deletion will take O(n) for shifting elements to rearrange the Queue)
+- Access - O(n)
+- Search - O(n)
+
+### More on this topic
+- https://en.wikipedia.org/wiki/Queue_(abstract_data_type)
+- https://www.tutorialspoint.com/data_structures_algorithms/dsa_queue.htm
+- https://en.wikibooks.org/wiki/Data_Structures/Stacks_and_Queues

Data Structure/Queue/queue.py

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+""" Queue implementation using Python List """
+
+class Queue(object):
+
+    def __init__(self):
+        self.items = []
+
+    def isEmpty(self):
+        return (self.items == [])
+
+    def enqueue(self, item):
+        self.items.append(item)
+
+    def peek(self):
+        return self.items[0]
+
+    def dequeue(self):
+        if self.isEmpty():
+            return None
+        return self.items.pop(0) #pops the first element from the list

Data Structure/Queue/queue.svg

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+from queue import Queue
+
+queue = Queue()
+queue.enqueue(10)
+queue.enqueue(15)
+
+print(queue.isEmpty())
+print(queue.peek())
+print(queue.dequeue())
+print(queue.dequeue())
+print(queue.dequeue())
+print(queue.isEmpty())