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
}