Valid Number

 1 class Solution {
 2 public:
 3     bool isNumber( const char *s ) {
 4         return ParseDecimal( s ) && ParseScientific( s ) && *s == ‘\0‘;
 5     }
 6 private:
 7     bool ParseDigits( const char* &s ) {
 8         if( *s < ‘0‘ || *s > ‘9‘ ) { return false; }
 9         while( *s >= ‘0‘ && *s <= ‘9‘ ) { ++s; }
10         return true;
11     }
12     bool ParseDecimal( const char* &s ) {
13         while( *s == ‘ ‘ ) { ++s; }
14         if( *s == ‘+‘ || *s == ‘-‘ ) {
15             if( *(++s) == ‘\0‘ ) { return false; }
16         }
17         bool flag1 = ParseDigits( s );
18         if( *s == ‘.‘ ) { ++s; }
19         bool flag2 = ParseDigits( s );
20         return flag1 || flag2;
21     }
22     bool ParseScientific( const char* &s ) {
23         if( *s == ‘e‘ ) {
24             ++s;
25             if( *s == ‘+‘ || *s == ‘-‘ ) {
26                 if( *(++s) == ‘\0‘ ) { return false; }
27             }
28             if( !ParseDigits( s ) ) { return false; };
29         }
30         while( *s == ‘ ‘ ) { ++s; }
31         return true;
32     }
33 };