'''Jaro distance'''

from __future__ import division


def jaro(s, t):
    '''Jaro distance between two strings.'''
    s_len = len(s)
    t_len = len(t)

    if s_len == 0 and t_len == 0:
        return 1

    match_distance = (max(s_len, t_len) // 2) - 1

    s_matches = [False] * s_len
    t_matches = [False] * t_len

    matches = 0
    transpositions = 0

    for i in range(s_len):
        start = max(0, i - match_distance)
        end = min(i + match_distance + 1, t_len)

        for j in range(start, end):
            if t_matches[j]:
                continue
            if s[i] != t[j]:
                continue
            s_matches[i] = True
            t_matches[j] = True
            matches += 1
            break

    if matches == 0:
        return 0

    k = 0
    for i in range(s_len):
        if not s_matches[i]:
            continue
        while not t_matches[k]:
            k += 1
        if s[i] != t[k]:
            transpositions += 1
        k += 1

    return ((matches / s_len) +
            (matches / t_len) +
            ((matches - transpositions / 2) / matches)) / 3


def main():
    '''Tests'''

    for s, t in [('MARTHA', 'MARHTA'),
                 ('DIXON', 'DICKSONX'),
                 ('JELLYFISH', 'SMELLYFISH')]:
        print("jaro(%r, %r) = %.10f" % (s, t, jaro(s, t)))


if __name__ == '__main__':
    main()