# 1608. Special Array With X Elements Greater Than or Equal X

Easy
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.
Constraints:
• `1 <= nums.length <= 100`
• `0 <= nums[i] <= 1000`

### 解題

func specialArray(nums []int) int {
m := make(map[int]bool)
sort.Ints(nums)
for i, num := range nums {
n := num
for n > len(nums) - i {
if m[n] == true { break }
n--
}
if n == len(nums) - i && m[n] == false {
return len(nums) - i
}
m[num] = true
}
return -1
}