first-missing-positive

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Algorithms

Given an unsorted integer array <code>nums</code>. Return the smallest positive integer that is not present in <code>nums</code>.

You must implement an algorithm that runs in <code>O(n)</code> time and uses <code>O(1)</code> auxiliary space.

&nbsp;
Example 1:

<pre>
Input: nums = [1,2,0]
Output: 3
Explanation: The numbers in the range [1,2] are all in the array.
</pre>

Example 2:

<pre>
Input: nums = [3,4,-1,1]
Output: 2
Explanation: 1 is in the array but 2 is missing.
</pre>

Example 3:

<pre>
Input: nums = [7,8,9,11,12]
Output: 1
Explanation: The smallest positive integer 1 is missing.
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= nums.length &lt;= 105</code></li>
	<li><code>-231 &lt;= nums[i] &lt;= 231 - 1</code></li>
</ul>