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Evenly spaced, while they are trees solution in Clear category for Find Evenly Spaced Trees by Phil15
import itertools as it
def find_evenly_spaced_trees(trees: list[int]) -> int | None:
# if diff is larger than this, then we can't have 3 evenly spaced trees.
diff_limit = (max(trees) - min(trees)) // 2
is_tree = frozenset(trees).__contains__
best = max(
len([*it.takewhile(is_tree, evenly_spaced)])
# evenly_spaced = (a_tree, a_tree + diff, a_tree + diff * 2, ...)
for evenly_spaced in it.starmap(it.count, it.product(trees, range(1, diff_limit + 1)))
)
return None if best <= 2 else best
June 26, 2024