Which of the following problems is not NP-hard?

Complexity of Kruskal’s algorithm for finding the minimum spanning tree of an undirected graph containing n vertices and m edges if the edges are sorted is _______.

Assume that the last element of the set is used as partition element in Quicksort. If n distinct elements from the set [1…n] are to be sorted, give an input for which Quicksort takes maximum time.

Following algorithm(s) can be used to sort n integers in the range [1....... n³] in O(n) time