Learnt Queue from the book

Author: MayankShah1

.idea/workspace.xml

@@ -0,0 +1,63 @@
+class Empty(Exception):
+    """Error attempting to access an element from an empty container"""
+    pass
+
+class ArrayQueue:
+    """FIFO Queue implementation using Python list as underlying storage."""
+
+    DEFAULT_CAPACITY = 10
+
+    def __init__(self):
+        """Create an empty queue."""
+
+        self._data = [None]*ArrayQueue.DEFAULT_CAPACITY
+        self._size = 0
+        self._front = 0
+
+    def __len__(self):
+        """Return the number of elements in queue."""
+        return self._size
+
+    def is_empty(self):
+        """Return True if the queue is empty."""
+        return self._size == 0
+
+    def first(self):
+        """Return the element at the front of the queue.
+        
+        Raise an exception if queue is empty.
+        """
+        if self.is_empty():
+            raise Empty('Queue is empty')
+        return self._data[self._front]
+
+    def dequeue(self):
+        """Remove and return the first element of the queue.
+        
+        Raise Empty exception is queue is empty.
+        """
+        if self.is_empty():
+            raise Empty('Queue is empty')
+        answer = self._data[self._front]
+        self._data[self._front] = None
+        self._front = (self._front + 1) % len(self._data)
+        self._size -= 1
+        return answer
+
+    def enqueue(self, e):
+        """Add an element to back of queue."""
+        if self._size == len(self._data):
+            self._resize(2 * len(self._data))
+        avail = (self._size + self._front) % len(self._data)
+        self._data[avail] = e
+        self._size += 1
+
+    def _resize(self, cap):
+        """Resize to a new list of capacity >= len(self)"""
+        old = self._data
+        self._data = [None]*cap
+        walk = self._front
+        for k in range(self._size):
+            self._data[k] = old[walk]
+            walk = (1 + walk) % len(old)
+        self._front = 0