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67 lines
3.0 KiB
HTML
67 lines
3.0 KiB
HTML
<p>You are given an integer array <code>target</code> and an integer <code>n</code>.</p>
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<p>You have an empty stack with the two following operations:</p>
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<ul>
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<li><strong><code>"Push"</code></strong>: pushes an integer to the top of the stack.</li>
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<li><strong><code>"Pop"</code></strong>: removes the integer on the top of the stack.</li>
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</ul>
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<p>You also have a stream of the integers in the range <code>[1, n]</code>.</p>
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<p>Use the two stack operations to make the numbers in the stack (from the bottom to the top) equal to <code>target</code>. You should follow the following rules:</p>
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<ul>
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<li>If the stream of the integers is not empty, pick the next integer from the stream and push it to the top of the stack.</li>
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<li>If the stack is not empty, pop the integer at the top of the stack.</li>
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<li>If, at any moment, the elements in the stack (from the bottom to the top) are equal to <code>target</code>, do not read new integers from the stream and do not do more operations on the stack.</li>
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</ul>
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<p>Return <em>the stack operations needed to build </em><code>target</code> following the mentioned rules. If there are multiple valid answers, return <strong>any of them</strong>.</p>
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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> target = [1,3], n = 3
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<strong>Output:</strong> ["Push","Push","Pop","Push"]
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<strong>Explanation:</strong> Initially the stack s is empty. The last element is the top of the stack.
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Read 1 from the stream and push it to the stack. s = [1].
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Read 2 from the stream and push it to the stack. s = [1,2].
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Pop the integer on the top of the stack. s = [1].
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Read 3 from the stream and push it to the stack. s = [1,3].
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> target = [1,2,3], n = 3
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<strong>Output:</strong> ["Push","Push","Push"]
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<strong>Explanation:</strong> Initially the stack s is empty. The last element is the top of the stack.
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Read 1 from the stream and push it to the stack. s = [1].
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Read 2 from the stream and push it to the stack. s = [1,2].
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Read 3 from the stream and push it to the stack. s = [1,2,3].
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</pre>
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<p><strong class="example">Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> target = [1,2], n = 4
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<strong>Output:</strong> ["Push","Push"]
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<strong>Explanation:</strong> Initially the stack s is empty. The last element is the top of the stack.
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Read 1 from the stream and push it to the stack. s = [1].
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Read 2 from the stream and push it to the stack. s = [1,2].
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Since the stack (from the bottom to the top) is equal to target, we stop the stack operations.
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The answers that read integer 3 from the stream are not accepted.
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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 <= target.length <= 100</code></li>
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<li><code>1 <= n <= 100</code></li>
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<li><code>1 <= target[i] <= n</code></li>
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<li><code>target</code> is strictly increasing.</li>
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</ul>
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