gistfile1.txt

def numDecodings(s: str) -> int:
    if(not s):return 1
    elif(len(s)==1):
        if(s=="0"):return 0
        else:return 1
            
    if(s[0]=="0"):return 0
    prev=1
    cur=0 if s[1]=="0" else 1
    if(int(s[:2])<=26): cur+=1
        
    for i in range(2,len(s)):
        if(s[i]!="0"):temp=cur
        else:temp=0
        if(s[i-1]!="0" and int(s[i-1:i+1])<=26):temp+=prev
                
        prev,cur=cur,temp
    return cur

================================================================================

from functools import lru_cache

@lru_cache(maxsize=None)
def numDecodings(self, s: str) -> int:
    if not s:
        return 1

    single = 0
    if '1' <= s[0] and s[0] <= '9':
        single = self.numDecodings(s[1:])

    double = 0
    if 10 <= int(s[:2]) and int(s[:2]) <= 26:
        double = self.numDecodings(s[2:])

    return single + double