970. Powerful Integers

Problem

Given three integers x, y, and bound, return **a list of all the *powerful integers* that have a value less than or equal to** bound.

An integer is powerful if it can be represented as xi + yj for some integers i >= 0 and j >= 0.

You may return the answer in any order. In your answer, each value should occur at most once.

  Example 1:

Input: x = 2, y = 3, bound = 10
Output: [2,3,4,5,7,9,10]
Explanation:
2 = 20 + 30
3 = 21 + 30
4 = 20 + 31
5 = 21 + 31
7 = 22 + 31
9 = 23 + 30
10 = 20 + 32

Example 2:

Input: x = 3, y = 5, bound = 15
Output: [2,4,6,8,10,14]

  Constraints:

• 1 <= x, y <= 100

• 0 <= bound <= 10^6

Solution (Java)

class Solution {
    public List<Integer> powerfulIntegers(int x, int y, int bound) {
        int iBound = (x == 1 ? 1 : (int) (Math.log10(bound) / Math.log10(x)));
        int jBound = (y == 1 ? 1 : (int) (Math.log10(bound) / Math.log10(y)));
        HashSet<Integer> set = new HashSet<>();
        for (int i = 0; i <= iBound; i++) {
            for (int j = 0; j <= jBound; j++) {
                int number = (int) (Math.pow(x, i) + Math.pow(y, j));
                if (number <= bound) {
                    set.add(number);
                }
            }
        }
        return new ArrayList<>(set);
    }
}

Explain:

nope.

Complexity:

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