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52 lines
2.7 KiB
HTML
52 lines
2.7 KiB
HTML
<p>Design a queue that supports <code>push</code> and <code>pop</code> operations in the front, middle, and back.</p>
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<p>Implement the <code>FrontMiddleBack</code> class:</p>
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<ul>
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<li><code>FrontMiddleBack()</code> Initializes the queue.</li>
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<li><code>void pushFront(int val)</code> Adds <code>val</code> to the <strong>front</strong> of the queue.</li>
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<li><code>void pushMiddle(int val)</code> Adds <code>val</code> to the <strong>middle</strong> of the queue.</li>
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<li><code>void pushBack(int val)</code> Adds <code>val</code> to the <strong>back</strong> of the queue.</li>
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<li><code>int popFront()</code> Removes the <strong>front</strong> element of the queue and returns it. If the queue is empty, return <code>-1</code>.</li>
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<li><code>int popMiddle()</code> Removes the <strong>middle</strong> element of the queue and returns it. If the queue is empty, return <code>-1</code>.</li>
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<li><code>int popBack()</code> Removes the <strong>back</strong> element of the queue and returns it. If the queue is empty, return <code>-1</code>.</li>
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</ul>
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<p><strong>Notice</strong> that when there are <b>two</b> middle position choices, the operation is performed on the <strong>frontmost</strong> middle position choice. For example:</p>
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<ul>
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<li>Pushing <code>6</code> into the middle of <code>[1, 2, 3, 4, 5]</code> results in <code>[1, 2, <u>6</u>, 3, 4, 5]</code>.</li>
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<li>Popping the middle from <code>[1, 2, <u>3</u>, 4, 5, 6]</code> returns <code>3</code> and results in <code>[1, 2, 4, 5, 6]</code>.</li>
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</ul>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<pre>
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<strong>Input:</strong>
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["FrontMiddleBackQueue", "pushFront", "pushBack", "pushMiddle", "pushMiddle", "popFront", "popMiddle", "popMiddle", "popBack", "popFront"]
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[[], [1], [2], [3], [4], [], [], [], [], []]
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<strong>Output:</strong>
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[null, null, null, null, null, 1, 3, 4, 2, -1]
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<strong>Explanation:</strong>
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FrontMiddleBackQueue q = new FrontMiddleBackQueue();
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q.pushFront(1); // [<u>1</u>]
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q.pushBack(2); // [1, <u>2</u>]
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q.pushMiddle(3); // [1, <u>3</u>, 2]
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q.pushMiddle(4); // [1, <u>4</u>, 3, 2]
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q.popFront(); // return 1 -> [4, 3, 2]
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q.popMiddle(); // return 3 -> [4, 2]
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q.popMiddle(); // return 4 -> [2]
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q.popBack(); // return 2 -> []
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q.popFront(); // return -1 -> [] (The queue is empty)
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 <= val <= 10<sup>9</sup></code></li>
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<li>At most <code>1000</code> calls will be made to <code>pushFront</code>, <code>pushMiddle</code>, <code>pushBack</code>, <code>popFront</code>, <code>popMiddle</code>, and <code>popBack</code>.</li>
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</ul>
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