java.lang.Object
g0201_0300.s0232_implement_queue_using_stacks.MyQueue

public class MyQueue extends Object
232 - Implement Queue using Stacks.<p>Easy</p> <p>Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (<code>push</code>, <code>peek</code>, <code>pop</code>, and <code>empty</code>).</p> <p>Implement the <code>MyQueue</code> class:</p> <ul> <li><code>void push(int x)</code> Pushes element x to the back of the queue.</li> <li><code>int pop()</code> Removes the element from the front of the queue and returns it.</li> <li><code>int peek()</code> Returns the element at the front of the queue.</li> <li><code>boolean empty()</code> Returns <code>true</code> if the queue 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 stack, which means only <code>push to top</code>, <code>peek/pop from top</code>, <code>size</code>, and <code>is empty</code> operations are valid.</li> <li>Depending on your language, the stack may not be supported natively. You may simulate a stack using a list or deque (double-ended queue) as long as you use only a stack&rsquo;s standard operations.</li> </ul> <p><strong>Example 1:</strong></p> <p><strong>Input:</strong></p> <pre><code> [&quot;MyQueue&quot;, &quot;push&quot;, &quot;push&quot;, &quot;peek&quot;, &quot;pop&quot;, &quot;empty&quot;] [ [], [1], [2], [], [], []] </code></pre> <p><strong>Output:</strong></p> <pre><code> [null, null, null, 1, 1, false] </code></pre> <p><strong>Explanation:</strong></p> <pre><code> MyQueue myQueue = new MyQueue(); myQueue.push(1); // queue is: [1] myQueue.push(2); // queue is: [1, 2] (leftmost is front of the queue) myQueue.peek(); // return 1 myQueue.pop(); // return 1, queue is [2] myQueue.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>peek</code>, and <code>empty</code>.</li> <li>All the calls to <code>pop</code> and <code>peek</code> are valid.</li> </ul> <p><strong>Follow-up:</strong> Can you implement the queue such that each operation is <strong><a href="https://en.wikipedia.org/wiki/Amortized_analysis" target="_top">amortized</a></strong> <code>O(1)</code> time complexity? In other words, performing <code>n</code> operations will take overall <code>O(n)</code> time even if one of those operations may take longer.</p>
  • Constructor Details Link icon

    • MyQueue Link icon

      public MyQueue()
  • Method Details Link icon

    • push Link icon

      public void push(int x)
    • pop Link icon

      public int pop()
    • peek Link icon

      public int peek()
    • empty Link icon

      public boolean empty()