# 1608. 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:

Input: nums = \[3,5] Output: 2 Explanation: There are 2 values (3 and 5) that are greater than or equal to 2. Example 2:

Input: nums = \[0,0] Output: -1 Explanation: No numbers fit the criteria for x. If x = 0, there should be 0 numbers >= x, but there are 2. If x = 1, there should be 1 number >= x, but there are 0. If x = 2, there should be 2 numbers >= x, but there are 0. x cannot be greater since there are only 2 numbers in nums. Example 3:

Input: nums = \[0,4,3,0,4] Output: 3 Explanation: There are 3 values that are greater than or equal to 3. Example 4:

Input: nums = \[3,6,7,7,0] Output: -1

Constraints:

1 <= nums.length <= 100 0 <= nums\[i] <= 1000

## Solutions

1. **sort O(nlog(n))**

```cpp
class Solution {
public:
    int specialArray(vector<int>& nums) {
        nums.push_back(INT_MIN);
        sort(nums.rbegin(), nums.rend());
        for (int i = 0; i < nums.size() - 1; i++) {
            if (i + 1 <= nums[i] && i + 1 > nums[i + 1])
                return i + 1;
        }

        return -1;
    }
};
```