[leetcode] Valid Number

Validate if a given string is numeric.

Some examples:
"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

class Solution {
public:
    bool isNumber(const char *s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int i=0;
        bool dotappeared=false;
        bool numberappeared=false;
        bool eappeared=false;
        for( ; s[i]==' ' ; i++);
        if(s[i]=='+' || s[i]=='-')
            i++;
        if(s[i]=='\0')
            return false;
        for( ; s[i] ; i++){
    		switch(s[i]){
			case ' ':
				for( ; s[i] && s[i]==' ' ; i++);
                if(s[i]!='\0')
                    return false;
                i--;
				break;
			case '.':
				if(dotappeared)
					return false;
                if(eappeared)
                    return false;
				dotappeared=true;
				break;
			case 'e':
			case 'E':
				if(!numberappeared || eappeared)
					return false;
				eappeared=true;
				dotappeared=false;
				numberappeared=false;
                if(s[i+1]=='-' || s[i+1]=='+')
                    i++;
				break;
			case '0':
			case '1':
			case '2':
			case '3':
			case '4':
			case '5':
			case '6':
			case '7':
			case '8':
			case '9':
				numberappeared=true;
				break;
			default:
				return false;
			}
		}
        if(!numberappeared)
            return false;
        return true;
    }
};