Implement Stack using Queues

Author: anantkaushik

225-implement-stack-using-queues.py

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+"""
+Problem Link: https://leetcode.com/problems/implement-stack-using-queues/
+
+Implement the following operations of a stack using queues.
+push(x) -- Push element x onto stack.
+pop() -- Removes the element on top of the stack.
+top() -- Get the top element.
+empty() -- Return whether the stack is empty.
+
+Example:
+MyStack stack = new MyStack();
+
+stack.push(1);
+stack.push(2);  
+stack.top();   // returns 2
+stack.pop();   // returns 2
+stack.empty(); // returns false
+
+Notes:
+You must use only standard operations of a queue -- which means only push to back, 
+peek/pop from front, size, and is empty operations are valid.
+Depending on your language, queue may not be supported natively. 
+You may simulate a queue by using a list or deque (double-ended queue), 
+as long as you use only standard operations of a queue.
+You may assume that all operations are valid 
+(for example, no pop or top operations will be called on an empty stack).
+"""
+# Time Complexity: Push - O(n), Pop, Top, Empty - O(1)
+class MyStack:
+
+    def __init__(self):
+        """
+        Initialize your data structure here.
+        """
+        self.q = []
+
+        
+    def push(self, x: int) -> None:
+        """
+        Push element x onto stack.
+        """
+        self.q.append(x)
+        for i in range(len(self.q)-1):
+          self.q.append(self.q.pop(0))
+
+
+    def pop(self) -> int:
+        """
+        Removes the element on top of the stack and returns that element.
+        """
+        return self.q.pop(0)
+        
+
+    def top(self) -> int:
+        """
+        Get the top element.
+        """
+        return self.q[0]
+
+
+    def empty(self) -> bool:
+        """
+        Returns whether the stack is empty.
+        """
+        return not self.q
+         
+
+
+# Your MyStack object will be instantiated and called as such:
+# obj = MyStack()
+# obj.push(x)
+# param_2 = obj.pop()
+# param_3 = obj.top()
+# param_4 = obj.empty()