What will be time Complexity for Displaying data in alphabetical order using skip-list ? and what time complexity will be for skip list if we implement using quad node ?
Let's assume that you have the input that contains N elements. Firstly you have to construct a skip-list. The complexity of a single insert operation is O(log N) in average so the complexity of inserting N elements would be O(N * log N). When the skip-list is constructed then elements within this list are sorted. So in order to enumerate them you only need to visit each element what is O(N).
It is worth saying that the skip-list is based on randomness. It means that O(log N) complexity of a single insert operation is not guaranteed. The worst case complexity is O(N), It means that in the worst case the complexity of inserting N elements into the skip-list would be O(N^2).