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

Description

https://leetcode.com/problems/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

Explanation

Start with x = 0 and increase x to a most len(nums), and check if the total number of elements in list is equal to x.

Python Solution

class Solution:
    def specialArray(self, nums: List[int]) -> int:
                
        x = 0
        
        while x <= len(nums):
            count = 0
            for num in nums:
                if num >= x:
                    count += 1

            if count == x:
                return x
            
            x += 1
        
        return -1
  • Time Complexity: O(N^N).
  • Space Complexity: O(1).

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