str_subarray

def find_k_subseq(k, a, b):
    b_subs = set([''.join(map(chr, b[i:i + k])) for i in range(len(b) - k + 1)])
    for i in range(len(a) - k + 1):
        a_sub = ''.join(map(chr, a[i:i + 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