Package g0201_0300.s0225_implement_stack_using_queues

Class MyStack

java.lang.Object
g0201_0300.s0225_implement_stack_using_queues.MyStack
public class MyStack extends Object
225 - Implement Stack using Queues.<p>Easy</p> <p>Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (<code>push</code>, <code>top</code>, <code>pop</code>, and <code>empty</code>).</p> <p>Implement the <code>MyStack</code> class:</p> <ul> <li><code>void push(int x)</code> Pushes element x to the top of the stack.</li> <li><code>int pop()</code> Removes the element on the top of the stack and returns it.</li> <li><code>int top()</code> Returns the element on the top of the stack.</li> <li><code>boolean empty()</code> Returns <code>true</code> if the stack is empty, <code>false</code> otherwise.</li> </ul> <p><strong>Notes:</strong></p> <ul> <li>You must use <strong>only</strong> standard operations of a queue, which means that only <code>push to back</code>, <code>peek/pop from front</code>, <code>size</code> and <code>is empty</code> operations are valid.</li> <li>Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue&rsquo;s standard operations.</li> </ul> <p><strong>Example 1:</strong></p> <p><strong>Input</strong> [&ldquo;MyStack&rdquo;, &ldquo;push&rdquo;, &ldquo;push&rdquo;, &ldquo;top&rdquo;, &ldquo;pop&rdquo;, &ldquo;empty&rdquo;] [ [], [1], [2], [], [], []]</p> <p><strong>Output:</strong> [null, null, null, 2, 2, false]</p> <p><strong>Explanation:</strong></p> <pre><code> MyStack myStack = new MyStack(); myStack.push(1); myStack.push(2); myStack.top(); // return 2 myStack.pop(); // return 2 myStack.empty(); // return False </code></pre> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= x <= 9</code></li> <li>At most <code>100</code> calls will be made to <code>push</code>, <code>pop</code>, <code>top</code>, and <code>empty</code>.</li> <li>All the calls to <code>pop</code> and <code>top</code> are valid.</li> </ul> <p><strong>Follow-up:</strong> Can you implement the stack using only one queue?</p>

  • Constructor Details

    • MyStack

      public MyStack()

  • Method Details

    • push

      public void push(int x)

    • pop

      public int pop()

    • top

      public int top()

    • empty

      public boolean empty()