decode-ways.py

class Solution:
    
    num_to_alpha_dict = {str(num): chr( ord("A") + num-1 ) for num in range(1,27)}    
    ways = 0
    
    # Dictionary for memoization
    ways_dict = dict()
    
    def decode_message(self, s):
        
        current_ways = self.ways

        if s == "":
            self.ways += 1
            return
        
        if s in self.ways_dict:
            self.ways += self.ways_dict[s]
            return
        
        if s[0] in self.num_to_alpha_dict:
            self.decode_message(s[1:])
        
        if len(s) >= 2 and s[0:2] in self.num_to_alpha_dict:
            self.decode_message(s[2:])
        
        if self.ways > current_ways:
            self.ways_dict[s] = self.ways - current_ways
    
    def numDecodings(self, s: str) -> int:    
        
        self.decode_message(s)
        
        print(self.ways_dict)

        return self.ways
        
def main():
    solution = Solution()
    input_string = "12345"

    print("Input:", input_string)

    print("Answer:", solution.numDecodings(input_string))

if __name__ == "__main__":
    main()