Special Array With X Elements Greater Than or Equal X

The problem is looking for a specific number x that has a special property. This property is defined by the condition that there are exactly x numbers in the nums array that are greater than or equal to x.

In other words, x is the count of numbers in nums which are greater than or equal to x.

Let’s clarify it further with an example:

If we have nums = [3, 5], the output is 2 because there are 2 numbers (which are 3 and 5) in nums that are greater than or equal to 2.

But if nums = [0,0], the output is -1 because there’s no x that satisfies the condition. Here’s why:

• If x = 0, there should be 0 numbers greater than or equal to 0, but there are 2.
• If x = 1, there should be 1 number greater than or equal to 1, but there are 0.
• If x = 2, there should be 2 numbers greater than or equal to 2, but there are 0.

So, we’re looking for a number x that is equal to the count of numbers that are greater than or equal to x in the nums array. If there’s no such number, we return -1.

The logic of the problem requires us to find a number x such that exactly x numbers in nums are greater than or equal to x. If no such number is found, then we should return -1.

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from typing import List

class Solution:
    def specialArray(self, nums: List[int]) -> int:
        # Iterate from 0 to the length of nums
        for x in range(len(nums) + 1):
            # If x = 0, ensure there are no elements in nums
            if x == 0 and len(nums) > 0:
                continue
            # Count the numbers greater than or equal to x
            count = sum(1 for i in nums if i >= x)
            # If count is equal to x, return x
            if count == x:
                return x
        # If no x found, return -1
        return -1

This code correctly handles the x = 0 case by ensuring that nums should be an empty array in this case. For other values of x, it counts the numbers in nums that are greater than or equal to x and checks if this count is equal to x. If such an x is found, it returns x. If no such x is found after checking all possible values, it returns -1.

Beginner friendly version:

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from typing import List

class Solution:
    def specialArray(self, nums: List[int]) -> int:
        for x in range(len(nums) + 1):
            if x == 0 and len(nums) > 0:
                continue

            count = 0
            for i in nums:
                if i >= x:
                    count += 1

            if count == x:
                return x

        return -1

In this solution, the inner loop that counts the numbers greater than or equal to x is explicitly written out, and the increment of count is done as a separate step. This makes it easier to understand each step of the process.