Techniques

调和级数时间复杂度

The key is that

$$\frac{1}{1}+\frac{1}{2}+\dots+\frac{1}{n}=O(\log n)$$

This implies that if $v$ iterates over $1\sim n$, but during each iteration, we only have $n/v$ operations, then the overall time complexity is $O(n\log n)$.