Let $H$ be a finite collection of hash functions that map a universe $U$ of keys to $\{0,1,2, \ldots ,m-1\}$.
$H$ is said to be universal if for each pair of distinct keys, $(k, i) \in U$, the number of hash functions $h\in H$ for which $h(k)=n(i)$ is at most ________
- $\dfrac{∣H∣}{m^2}$
- $\dfrac{1}{m^2 \log m}$
- $\dfrac{∣H∣}{m^2}$
- $\dfrac{∣H∣}{m}$