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leetcode-problemset/leetcode/problem/build-an-array-with-stack-operations.html
2022-03-29 12:55:24 +08:00

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<p>You are given an array <code>target</code> and an integer <code>n</code>.</p>
<p>In each iteration, you will read a number from <code>list = [1, 2, 3, ..., n]</code>.</p>
<p>Build the <code>target</code> array using the following operations:</p>
<ul>
<li><code>&quot;Push&quot;</code>: Reads a new element from the beginning list, and pushes it in the array.</li>
<li><code>&quot;Pop&quot;</code>: Deletes the last element of the array.</li>
<li>If the target array is already built, stop reading more elements.</li>
</ul>
<p>Return <em>a list of the operations needed to build </em><code>target</code>. The test cases are generated so that the answer is <strong>unique</strong>.</p>
<p>&nbsp;</p>
<p><strong>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>
Read number 1 and automatically push in the array -&gt; [1]
Read number 2 and automatically push in the array then Pop it -&gt; [1]
Read number 3 and automatically push in the array -&gt; [1,3]
</pre>
<p><strong>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;]
</pre>
<p><strong>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> You only need to read the first 2 numbers and stop.
</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>