- 1 <= N <= 100000 unless the statement says a smaller limit. - Input is assumed valid unless the problem explicitly asks for validation. - Use O(N) or better whenever a direct traversal solution ...

result = [[0] * n for i in range(n)] # empty list of 0s for i, j in zip(range(n), range(n - 1, -1, -1)): # i counts up, j counts down ...