inaz2's answer

できました。
```
$ python -m doctest -v yakyu.py
Trying:
    yakyu("s")
Expecting:
    010
ok
Trying:
    yakyu("ss")
Expecting:
    010,020
ok
Trying:
    yakyu("sss")
Expecting:
    010,020,100
ok
Trying:
    yakyu("ssbs")
Expecting:
    010,020,021,100
ok
Trying:
    yakyu("bbb")
Expecting:
    001,002,003
ok
Trying:
    yakyu("ssbbb")
Expecting:
    010,020,021,022,023
ok
Trying:
    yakyu("ssbbbb")
Expecting:
    010,020,021,022,023,000
ok
Trying:
    yakyu("hsbhfhbh")
Expecting:
    000,010,011,000,010,000,001,000
ok
Trying:
    yakyu("bbssp")
Expecting:
    001,002,012,022,100
ok
Trying:
    yakyu("ppp")
Expecting:
    100,200,000
ok
Trying:
    yakyu("ppsbp")
Expecting:
    100,200,210,211,000
ok
Trying:
    yakyu("ssffpffssp")
Expecting:
    010,020,020,020,100,110,120,200,210,000
ok
1 items had no tests:
    yakyu
1 items passed all tests:
  12 tests in yakyu.yakyu
12 tests in 2 items.
12 passed and 0 failed.
Test passed.
```