85 lines
3.1 KiB
Python
85 lines
3.1 KiB
Python
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# This demonstrates classic dynamic programming and prioritizes explainability.
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# Of course all of this would have been cleaner and would perform the same if
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# we were to use recursion with memoization (e.g. @memoize.cache)
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import sys
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import collections
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import dataclasses
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@dataclasses.dataclass(frozen=True)
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class Entry:
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working: int
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broken: int
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def total(self):
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return self.working + self.broken
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def no_dot_between(l, start, end):
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return not any(c for c in l[start+1 : end] if c == ".")
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def process(springs, counts):
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# entries[(i,j)] = how many ways if we have only first i springs and j nums,
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# given if that one was chosen to be working or no.
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entries = collections.defaultdict(lambda: Entry(working=0, broken=0))
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# boundary conditions, when there's no spring and no count left
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entries[(-1, -1)] = Entry(working=1, broken=0)
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# boundary conditions, when there's no count left but still springs
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for i in range(len(springs)):
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entries[(i, -1)] = Entry(
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working=(entries[(i - 1, -1)].working
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if springs[i] in (".", "?")
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else 0),
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broken=0)
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# building the rest of the table
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for i in range(len(springs)):
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for j in range(len(counts)):
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prev_entry_if_working = entries[(i - 1, j)]
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prev_working_entry_if_broken = (
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entries[(i - counts[j], j - 1)].working
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if no_dot_between(springs, i-counts[j], i)
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else 0)
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if springs[i] == ".":
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entries[(i, j)] = Entry(
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working=(prev_entry_if_working.working +
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prev_entry_if_working.broken),
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broken=0)
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elif springs[i] == "#":
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entries[(i, j)] = Entry(
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working=0,
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broken=prev_working_entry_if_broken)
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elif springs[i] == '?':
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entries[(i, j)] = Entry(
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working=(prev_entry_if_working.working +
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prev_entry_if_working.broken),
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broken=prev_working_entry_if_broken)
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# import code; code.interact(
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# local=locals(),
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# banner=(f"springs[{i}]={springs[i]}, counts[{j}]={counts[j]} "
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# f".={prev_entry_if_working}, "
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# f"#={prev_working_entry_if_broken}\n"
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# f"--> ({i}, {j}) = {entries[(i, j)]}"),
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# exitmsg='')
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return entries[(len(springs) - 1, len(counts) - 1)].total()
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if __name__ == "__main__":
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with open(sys.argv[1], "rt") as f:
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lines = f.readlines()
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total = 0
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for line in lines:
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springs, counts = line.strip().split(" ")
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counts = [int(c) for c in counts.split(",")]
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# delete these next 2 lines to have part 1 back
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springs = "?".join([springs]*5)
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counts = counts*5
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n = process(springs, counts)
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# print(f"{n} <-- {springs}-{counts}")
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total += n
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print(f"total = {total}")
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