new_contents: class Solution:
      # @param s, a string
      # @return an integer
      def numDecodings(self, s):
          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)]
  
subject: Create DecodeWays_002.py