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# 思路1 dp 三指针法

所有的ugly number：

(1) 1×2, 2×2, 3×2, 4×2, 5×2, … 所有正整数 *2 (2) 1×3, 2×3, 3×3, 4×3, 5×3, … 所有正整数* 3 (3) 1×5, 2×5, 3×5, 4×5, 5×5, … 所有正整数 \* 5 We can find that every subsequence is the ugly-sequence itself (1, 2, 3, 4, 5, …) multiply 2, 3, 5.

我们只要用三个指针，把这些数按照大小顺序排列起来就行了。