I am working on 957. Prison Cells After N Days but getting timeout error for my code. as I assume my code should be 14+O(n-14) about O(n) am I right since after 14 run pattern will be repeated? and how can I improve my code?

        from collections import defaultdict
        step_map = defaultdict(list)
        for k in range(N):
            if tuple(cells) in step_map:
                cells = step_map[tuple(cells)]
                tmp = list()
                for i in range(1, 7):
                    tmp += [int(cells[i - 1] == cells[i + 1])]
                tmp = [0] + tmp + [0]
                step_map[tuple(cells)] = tmp
                cells = tmp
        return cells
  • 1
    \$\begingroup\$ You need to de-indent this code. \$\endgroup\$ – Reinderien Jul 6 at 18:08
  • 1
    \$\begingroup\$ the complexity time is 8*N*k (there are 8 cells not 7). in Big-O notation, it does not make sense to say 16 + O(n - 16)... it should be O(n). \$\endgroup\$ – rdllopes Jul 6 at 18:38

The important part

They want something below O(n). Using map is a good idea but actually you should find the cycles and return the right position on the cycle instead of computing line by line.

Spoiler (possible solution)


            if tuple(cells) in step_map:
                return  step_map[tuple(cells)]


            if tuple(cells) in step_map:
                cycle = list()
                head = tuple(cells)
                previous = head
                while True:
                    next_node = tuple(step_map[previous])
                    if next_node == head:
                        return list(cycle[(N - k) % len(cycle)])
                    previous = next_node

Old edit - Some small improvements

There are some O(m) operations multiple times...

For example:

 tmp = [0] + tmp + [0]

Python operation for that is O(m). Therefore, your solution is O(nm).

step_map[tuple(cells)] = tmp

this is also O(m).

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