91_decode_ways.py

class Solution:
    def numDecodings(self, s: str) -> int:
        if s[0] == '0':
            return 0
        dp = [1 for i in range(len(s)+1)]
        for i in range(1, len(s)):
            if int(s[i]) != 0:
                dp[i+1] = dp[i]
            else:
                dp[i+1] = 0
            if (i != 0) and (10 <= int(s[i-1:i+1]) <= 26):
                dp[i+1] += dp[i-1]
        return dp[-1]

'''
    This is my personal record of solving Leetcode Problems. 
    If you have any questions, please discuss them in [Issues](https://github.com/mengxinayan/leetcode/issues).
    Copyright (C) 2020-2022  mengxinayan

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
'''