CareerCup

looks like merging n sorted lists . k-waymerge could solve the problem

In python using list comprehensions:
arr = [[1,2],[3],[4,5]]
[num for elem in arr for num in elem]

>> [1,2,3,4,5]

Just to clarify, is it allowed to change the data structure? Or just implement like iterator to flattenly access to the elements?

public List<Integer> flattenList(List<List<Integer>> listOfList) {
		List<Integer> flattenList = new ArrayList<Integer>();
		
		for(List<Integer> list: listOfList) {
			flattenList.addAll(list);
		}
		return flattenList;
		
	}

public static List<T> FlattenList<T>(List<List<T>> inputList)
        {
            return inputList.SelectMany(x => x).ToList();
        }

l = [[1,2], [3], [2,4,5], [6], [4,5,7,4]]
l1 = list(l) #Copy of l
e = []

for i in l:
    l2 = l1.pop(l1.index(i))
    for j in l2:
        e.append(j)
        
print e

[item for ilist in lst for item in ilist]