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1552-build-an-array-with-stack-operations/README.md

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+<h2><a href="https://leetcode.com/problems/build-an-array-with-stack-operations">1552. Build an Array With Stack Operations</a></h2><h3>Medium</h3><hr><p>You are given an integer array <code>target</code> and an integer <code>n</code>.</p>
+
+<p>You have an empty stack with the two following operations:</p>
+
+<ul>
+	<li><strong><code>&quot;Push&quot;</code></strong>: pushes an integer to the top of the stack.</li>
+	<li><strong><code>&quot;Pop&quot;</code></strong>: removes the integer on the top of the stack.</li>
+</ul>
+
+<p>You also have a stream of the integers in the range <code>[1, n]</code>.</p>
+
+<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>
+
+<ul>
+	<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>
+	<li>If the stack is not empty, pop the integer at the top of the stack.</li>
+	<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>
+</ul>
+
+<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>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> target = [1,3], n = 3
+<strong>Output:</strong> [&quot;Push&quot;,&quot;Push&quot;,&quot;Pop&quot;,&quot;Push&quot;]
+<strong>Explanation:</strong> Initially the stack s is empty. The last element is the top of the stack.
+Read 1 from the stream and push it to the stack. s = [1].
+Read 2 from the stream and push it to the stack. s = [1,2].
+Pop the integer on the top of the stack. s = [1].
+Read 3 from the stream and push it to the stack. s = [1,3].
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> target = [1,2,3], n = 3
+<strong>Output:</strong> [&quot;Push&quot;,&quot;Push&quot;,&quot;Push&quot;]
+<strong>Explanation:</strong> Initially the stack s is empty. The last element is the top of the stack.
+Read 1 from the stream and push it to the stack. s = [1].
+Read 2 from the stream and push it to the stack. s = [1,2].
+Read 3 from the stream and push it to the stack. s = [1,2,3].
+</pre>
+
+<p><strong class="example">Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> target = [1,2], n = 4
+<strong>Output:</strong> [&quot;Push&quot;,&quot;Push&quot;]
+<strong>Explanation:</strong> Initially the stack s is empty. The last element is the top of the stack.
+Read 1 from the stream and push it to the stack. s = [1].
+Read 2 from the stream and push it to the stack. s = [1,2].
+Since the stack (from the bottom to the top) is equal to target, we stop the stack operations.
+The answers that read integer 3 from the stream are not accepted.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= target.length &lt;= 100</code></li>
+	<li><code>1 &lt;= n &lt;= 100</code></li>
+	<li><code>1 &lt;= target[i] &lt;= n</code></li>
+	<li><code>target</code> is strictly increasing.</li>
+</ul>