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
}