题目

Given three integers x, y, and bound, return a list of all the 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:

  1. Input: x = 2, y = 3, bound = 10
  2. Output: [2,3,4,5,7,9,10]
  3. Explanation:
  4. 2 = 20 + 30
  5. 3 = 21 + 30
  6. 4 = 20 + 31
  7. 5 = 21 + 31
  8. 7 = 22 + 31
  9. 9 = 23 + 30
  10. 10 = 20 + 32

Example 2:

  1. Input: x = 3, y = 5, bound = 15
  2. 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

  1. class Solution {
  2.     public List<Integer> powerfulIntegers(int x, int y, int bound) {
  3.         Set<Integer> hash = new HashSet<>();
  4.         for (int a = 1; a < bound; a *= x) {
  5.             for (int b = 1; a + b <= bound; b *= y) {
  6.                 hash.add(a + b);
  7.                 if (y == 1) break;
  8.             }
  9.             if (x == 1) break;
  10.         }
  11.         return new ArrayList<>(hash);
  12.     }
  13. }