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

Problem

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

Solution (Java)

class Solution {
    public int specialArray(int[] nums) {
        Arrays.sort(nums);
        int max = nums[nums.length - 1];
        for (int x = 1; x <= max; x++) {
            int found = 0;
            int i = nums.length - 1;
            while (i >= 0 && nums[i] >= x) {
                i--;
                found++;
            }
            if (found == x) {
                return x;
            }
        }
        return -1;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).