Given a list of list, we have to merge all sub-list having common elements. These type of problems are very frequent in College examinations and while solving coding competitions.

Below are some ways to achieve this.]

Sure! Here's a Python program that merges a list of lists by combining sublists that share at least one common element: 

def merge_lists(lst):
    merged = []
    while lst:
        sublist = lst.pop(0)
        i = 0
        while i < len(merged):
            if set(sublist) & set(merged[i]):
                sublist = list(set(sublist) | set(merged.pop(i)))
            else:
                i += 1
        merged.append(sublist)
    return merged

This function takes in a list of lists as its argument, and returns a new list where any sublists that share at least one element have been combined. It does this by iteratively popping sublists from the input list, and checking if they have any elements in common with any of the sublists already in the merged list. If a common element is found, the two sublists are merged together by taking the set union of their elements. If no common element is found, the current sublist is simply appended to the merged list.

Here's an example usage of this function: 

>>> lst = [[1, 2], [2, 3], [4, 5], [6, 7], [7, 8, 9]]
>>> merge_lists(lst)
[[1, 2, 3], [4, 5], [6, 7, 8, 9]]

In this example, the sublists [1, 2] and [2, 3] share the common element 2, so they are merged together into [1, 2, 3]. Similarly, the sublists [6, 7] and [7, 8, 9] share the common element 7, so they are merged together into [6, 7, 8, 9]. The resulting merged list has three sublists with no common elements between them.