Bucket排序的复杂性（统一密钥）

Question

http://en.wikipedia.org/wiki/Sorting_algorithm#Comparison_of_algorithms

The following table describes integer sorting algorithms and other sorting algorithms that are not comparison sorts. As such, they are not limited by a \Omega(n \log n) lower bound. Complexities below assume n items to be sorted, with keys of size k, digit size d, and r the range of numbers to be sorted. Many of them are based on the assumption that the key size is large enough that all entries have unique key values, and hence that n << 2k, where << means "much less than."

k对于Bucket排序（统一密钥）是什么意思？

r对于Bucket排序（整数键）是什么意思？为什么复杂性会受到要排序的数字范围的影响？

为什么他们不同？