给定两个正整数 x 和 y，如果某一整数等于 x^i + y^j，其中整数 i >= 0 且 j >= 0，那么我们认为该整数是一个强整数。

返回值小于或等于 bound 的所有强整数组成的列表。

你可以按任何顺序返回答案。在你的回答中，每个值最多出现一次。

示例 1：

输入：x = 2, y = 3, bound = 10
输出：[2,3,4,5,7,9,10]
解释： 
2 = 2^0 + 3^0
3 = 2^1 + 3^0
4 = 2^0 + 3^1
5 = 2^1 + 3^1
7 = 2^2 + 3^1
9 = 2^3 + 3^0
10 = 2^0 + 3^2

示例 2：

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

提示：

• 1 <= x <= 100
• 1 <= y <= 100
• 0 <= bound <= 10^6

class Solution {
public:
    vector<int> powerfulIntegers(int x, int y, int bound) {
        set<int> num;
        if (x != 1 && y != 1) {
            for (int i = 0; i <= log(bound) / log(x); i++) {
                for (int j = 0; j <= log(bound - pow(x, i) / log(y)); j++) {
                    if (bound >= pow(x, i) + pow(y, j))
                        num.insert(pow(x, i) + pow(y, j));
                }
            }
        } else if (x == 1 && y == 1) {
            if (bound >= 2)
                num.insert(2);
        } else if (x == 1) {
            for (int j = 0; j <= log(bound - 1) / log(y); j++) {
                num.insert(pow(y, j) + 1);
            }
        } else {
            for (int i = 0; i <= log(bound - 1) / log(x); i++) {
                num.insert(pow(x, i) + 1);
            }
        }
        vector<int> ans;
        ans.assign(num.begin(), num.end());
        return ans;
    }
};

https://leetcode-cn.com/problems/powerful-integers/