See this line ""Concatenate the list B[0], B[1], ..., B[n – 1] together in order"".
This Algorithm is implementing a bucket sort, in which the input is divided into fixed length buckets.
Take for example => 34,109,349,233,567,895,234,456,245,.......
Now this input size can be divided into fixed length buckets of size 100 each and each bucket is sorted particularly, then as the last line suggests, concatenate all the buckets. Main thing lies that which algorithm are we going to use to sort a particular bucket.
Best case lies, when elements are uniformly distributed between the buckets.
Worst case lies, when all the elements are multiplexed into a single bucket. So, for a large input, sorting algorithm for this one bucket can lead to worst case sorting.
Bucket sort always uses stable sorting algorithm for sorting a particular bucket as a subroutine.
There are stable sorting algorithms available => Merge sort , Insertion sort , Bubble sort .
A). Merge sort Worst case O(N log N).
B). Insertion sort Worst case O(N2).
C). Bubble sort Worst case O(N2).
Now, stable sorting algorithm gives minimum WC complexity, is Merge sort.