easy short efficient clean code
\nclass Solution {\ntypedef long long ll;\npublic:\n    bool valid(const string&s){\n        ll h=stoll(s.substr(0, 2)), m=stoll(s.substr(3, 2));\n        retur
```\nclass Solution {\ntypedef long long ll;\npublic:\n    bool valid(const string&s){\n        ll h=stoll(s.substr(0, 2)), m=stoll(s.substr(3, 2));\n        return (h>=0 && h<=23 && m>=0 && m<=59);\n    }\n    int countTime(string&s, ll in=0) {\n        if(in==5){\n            return valid(s);\n        }\n        if(s[in]!=\'?\'){\n            return countTime(s,in+1);\n        }\n        ll ans=0;\n        for(ll i=0;i<=9;++i){\n            s[in]=\'0\'+i;\n            ans+=countTime(s, in+1);\n        }\n        s[in]=\'?\';\n        return ans;\n    }\n};\n```
['Recursion', 'C']