题解：
- Q1 https://leetcode.cn/problems/smallest-divisible-digit-product-i/solution/bao-li-mei-ju-zhi-duo-xun-huan-10-ci-pyt-ri4n/
- Q2 https://leetcode.cn/problems/maximum-frequency-of-an-element-after-performing-operations-i/solution/liang-chong-fang-fa-chai-fen-hua-dong-ch-spm9/
- Q3 https://leetcode.cn/problems/maximum-frequency-of-an-element-after-performing-operations-ii/solution/liang-chong-fang-fa-chai-fen-hua-dong-ch-7buy/
- Q4 https://leetcode.cn/problems/smallest-divisible-digit-product-ii/solution/bao-sou-zuo-fa-lei-si-shu-wei-dp-by-endl-nkoo/
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