0970. Powerful Integers (M)

Powerful Integers (M)

题目

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

题意

求所有小于等于bound的x幂与y幂之和。

思路

直接二重循环，用HashSet去重。

代码实现

Java

class Solution {
    public List<Integer> powerfulIntegers(int x, int y, int bound) {
        Set<Integer> hash = new HashSet<>();
        for (int a = 1; a < bound; a *= x) {
            for (int b = 1; a + b <= bound; b *= y) {
                hash.add(a + b);
                if (y == 1) break;
            }
            if (x == 1) break;
        }
        return new ArrayList<>(hash);
    }
}