partition_subarray

def find_k_subseq(k, a, b):
    b_subs = [b[ib:ib + k] for ib in range(len(b) - k + 1)]
    for ia in range(len(a) - k + 1):
        a_sub = a[ia:ia + k]
        if a_sub in b_subs:
            return True
    return False


def get_len(a, b):
    if len(a) > len(b):
        a, b = b, a
    lo = 0
    hi = len(a) + 1
    while lo < hi - 1:
        mid = (lo + hi) // 2
        if find_k_subseq(mid, a, b):
            lo = mid
        else:
            hi = mid
    return lo


a = [1, 2, 3, 4, 5]
b = [4, 5, 9]
assert (get_len(a, b) == 2)

a = [1, 2, 3, 2, 1]
b = [3, 2, 1, 5, 6]
assert (get_len(a, b) == 3)

assert (get_len([1], [1]) == 1)