LeetCode 3020: Find the Maximum Number of Elements in Subset Solution

Master LeetCode problem 3020 (Find the Maximum Number of Elements in Subset), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

3020. Find the Maximum Number of Elements in Subset

Medium

Array Hash Table Enumeration

Problem Explanation

Explanation:

To solve this problem, we need to identify the pattern that the selected subset should follow. The pattern is essentially a palindrome where the elements are arranged in a specific order: [x, x2, x4, ..., xk/2, xk, xk/2, ..., x4, x2, x]. This means that the elements on the left side of the array are mirrored by the elements on the right side.

We can approach this problem by iterating through each number in the array and checking if we can find a matching pair that satisfies the pattern condition. If we find a matching pair, we increment our count by 2. If the number itself is a perfect square, we can also include it in our count.

The time complexity of this approach is O(n) where n is the number of elements in the input array. The space complexity is O(1) as we are not using any additional data structures.

Solution Code

class Solution {
    public int maxElements(int[] nums) {
        int count = 0;
        for (int num : nums) {
            if (isPerfectSquare(num)) {
                count++;
            } else if (isPairPresent(nums, num)) {
                count += 2;
            }
        }
        return count;
    }
    
    private boolean isPerfectSquare(int num) {
        int sqrt = (int) Math.sqrt(num);
        return sqrt * sqrt == num;
    }
    
    private boolean isPairPresent(int[] nums, int num) {
        for (int n : nums) {
            if (n == num * num) {
                return true;
            }
        }
        return false;
    }
}

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