leetcode-problemset/leetcode/problem/special-array-with-x-elements-greater-than-or-equal-x.html

<p>You are given an array <code>nums</code> of non-negative integers. <code>nums</code> is considered <strong>special</strong> if there exists a number <code>x</code> such that there are <strong>exactly</strong> <code>x</code> numbers in <code>nums</code> that are <strong>greater than or equal to</strong> <code>x</code>.</p>

<p>Notice that <code>x</code> <strong>does not</strong> have to be an element in <code>nums</code>.</p>

<p>Return <code>x</code> <em>if the array is <strong>special</strong>, otherwise, return </em><code>-1</code>. It can be proven that if <code>nums</code> is special, the value for <code>x</code> is <strong>unique</strong>.</p>

<p>&nbsp;</p>
<p><strong>Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [3,5]
<strong>Output:</strong> 2
<strong>Explanation:</strong> There are 2 values (3 and 5) that are greater than or equal to 2.
</pre>

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

<pre>
<strong>Input:</strong> nums = [0,0]
<strong>Output:</strong> -1
<strong>Explanation:</strong> No numbers fit the criteria for x.
If x = 0, there should be 0 numbers &gt;= x, but there are 2.
If x = 1, there should be 1 number &gt;= x, but there are 0.
If x = 2, there should be 2 numbers &gt;= x, but there are 0.
x cannot be greater since there are only 2 numbers in nums.
</pre>

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

<pre>
<strong>Input:</strong> nums = [0,4,3,0,4]
<strong>Output:</strong> 3
<strong>Explanation:</strong> There are 3 values that are greater than or equal to 3.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 100</code></li>
	<li><code>0 &lt;= nums[i] &lt;= 1000</code></li>
</ul>