题目
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.
解题之法
class Solution {
public:
bool isNumber(string s) {
int i = 0;
// skip the whilespaces
for(; s[i] == ' '; i++) {}
// check the significand
if(s[i] == '+' || s[i] == '-') i++; // skip the sign if exist
int n_nm, n_pt;
for(n_nm=0, n_pt=0; (s[i]<='9' && s[i]>='0') || s[i]=='.'; i++)
s[i] == '.' ? n_pt++:n_nm++;
if(n_pt>1 || n_nm<1) // no more than one point, at least one digit
return false;
// check the exponent if exist
if(s[i] == 'e') {
i++;
if(s[i] == '+' || s[i] == '-') i++; // skip the sign
int n_nm = 0;
for(; s[i]>='0' && s[i]<='9'; i++, n_nm++) {}
if(n_nm<1)
return false;
}
// skip the trailing whitespaces
for(; s[i] == ' '; i++) {}
return s[i]==0; // must reach the ending 0 of the string
}
};
