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0442-find-all-duplicates-in-an-array/README.md

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+<h2><a href="https://leetcode.com/problems/find-all-duplicates-in-an-array/">442. Find All Duplicates in an Array</a></h2><h3>Medium</h3><hr><div><p>Given an integer array <code>nums</code> of length <code>n</code> where all the integers of <code>nums</code> are in the range <code>[1, n]</code> and each integer appears <strong>once</strong> or <strong>twice</strong>, return <em>an array of all the integers that appears <strong>twice</strong></em>.</p>
+
+<p>You must write an algorithm that runs in&nbsp;<code>O(n)&nbsp;</code>time and uses only constant extra space.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+<pre><strong>Input:</strong> nums = [4,3,2,7,8,2,3,1]
+<strong>Output:</strong> [2,3]
+</pre><p><strong class="example">Example 2:</strong></p>
+<pre><strong>Input:</strong> nums = [1,1,2]
+<strong>Output:</strong> [1]
+</pre><p><strong class="example">Example 3:</strong></p>
+<pre><strong>Input:</strong> nums = [1]
+<strong>Output:</strong> []
+</pre>
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>n == nums.length</code></li>
+	<li><code>1 &lt;= n &lt;= 10<sup>5</sup></code></li>
+	<li><code>1 &lt;= nums[i] &lt;= n</code></li>
+	<li>Each element in <code>nums</code> appears <strong>once</strong> or <strong>twice</strong>.</li>
+</ul>
+</div>