first-missing-positive.md

<p>Given an unsorted integer array, find the smallest missing&nbsp;positive integer.</p>

<p><strong>Example 1:</strong></p>

<pre>
Input: [1,2,0]
Output: 3
</pre>

<p><strong>Example 2:</strong></p>

<pre>
Input: [3,4,-1,1]
Output: 2
</pre>

<p><strong>Example 3:</strong></p>

<pre>
Input: [7,8,9,11,12]
Output: 1
</pre>

<p><strong>Note:</strong></p>

<p>Your algorithm should run in <em>O</em>(<em>n</em>) time and uses constant extra space.</p>