Decode Ways
Description:
A message containing letters from A-Z is being encoded to numbers using the following mapping:
‘A’ -> 1
‘B’ -> 2
…
‘Z’ -> 26
Given an encoded message containing digits, determine the total number of ways to decode it.
Example
Given encoded message 12, it could be decoded as AB (1 2) or L (12).
The number of ways decoding 12 is 2.
Code:
class Solution:
"""
@param s: a string, encoded message
@return: an integer, the number of ways decoding
"""
def numDecodings(self, s):
# write your code here
if s=="" or s[0]=='0': return 0
dp=[1,1]
for i in range(2,len(s)+1):
if 10 <=int(s[i-2:i]) <=26 and s[i-1]!='0':
dp.append(dp[i-1]+dp[i-2])
elif int(s[i-2:i])==10 or int(s[i-2:i])==20:
dp.append(dp[i-2])
elif s[i-1]!='0':
dp.append(dp[i-1])
else:
return 0
return dp[len(s)]