Leetcode
https://leetcode.com/problems/special-array-with-x-elements-greater-than-or-equal-x/
You are given an array nums of non-negative integers. nums is considered special if there exists a number x such that there are exactly x numbers in nums that are greater than or equal to x.
Notice that x does not have to be an element in nums.
Return x if the array is special, otherwise, return -1. It can be proven that if nums is special, the value for x is unique.
Example 1:
Example 2:
Example 3:
Example 4:
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