"""

```
def numDecodings(self, s):
"""
:type s: str
:rtype: int
"""
if not s or s[0] == '0': return 0
res = [1] * len(s)
for i in range(1,len(s)):
if s[i] == '0':
if s[i - 1] == '1' or s[i - 1] == '2':
res[i] = res[i - 2]
else:
return 0
elif s[i - 1] == '1' or s [i - 1] == '2' and s[i] < '7' :
res[i] = res[i - 2] + res[i - 1]
else:
res[i] = res[i - 1]
return res[-1]
```

"""