Added queue on stack

Author: ShyamW

data_structures/QueueOnList.py renamed to data_structures/Queue/QueueOnList.py

@@ -0,0 +1,51 @@
+"""Queue represented by a pseudo stack (represented by a list with pop and append)"""
+class Queue():
+    def __init__(self):
+        self.stack = []
+        self.length = 0
+
+    def __str__(self):
+        printed = '<' + str(self.stack)[1:-1] + '>'
+        return printed
+
+    """Enqueues {@code item}
+    @param item
+        item to enqueue"""
+    def put(self, item):
+        self.stack.append(item)
+        self.length = self.length + 1
+
+
+    """Dequeues {@code item}
+    @requirement: |self.length| > 0
+    @return dequeued
+        item that was dequeued"""
+    def get(self):
+        self.rotate(1)
+        dequeued = self.stack[self.length-1]
+        self.stack = self.stack[:-1]
+        self.rotate(self.length-1)
+        self.length = self.length -1
+        return dequeued
+
+    """Rotates the queue {@code rotation} times
+    @param rotation
+        number of times to rotate queue"""
+    def rotate(self, rotation):
+        for i in range(rotation):
+            temp = self.stack[0]
+            self.stack = self.stack[1:]
+            self.put(temp)
+            self.length = self.length - 1
+
+    """Reports item at the front of self
+    @return item at front of self.stack"""
+    def front(self):
+        front = self.get()
+        self.put(front)
+        self.rotate(self.length-1)
+        return front
+
+    """Returns the length of this.stack"""
+    def size(self):
+        return self.length