难点在于考虑周全,尝试了很多次,根据错误案例提示写全了
class Solution {
public:
bool isnum(string s) {
if (s[0] == '-' || s[0] == '+') return s.size() != 1 &&
((s[1] >= '0' && s[1] <= '9') || s[1] == '.') && isnum(string(s, 1, 999));
for (auto &x : s)
if (x<'0' || x>'9') return false;
return true;
}
bool isf(string s) {
if (s.empty()) return false;
if (s[0] == '-' || s[0] == '+') return s.size() != 1 &&
((s[1] >= '0' && s[1] <= '9') || s[1] == '.') && isf(string(s, 1, 999));
int k = s.find('.');
if (k == string::npos) return isnum(s);
else if (k == s.size() - 1) return s.size() != 1 && isnum(string(s, 0, k));
else return isnum(string(s, 0, k)) && s[k + 1] >= '0'&&s[k + 1] <= '9'&&isnum(string(s, k + 1, 999));
}
bool isNumber(string s) {
int t = 0;
while (t<s.size() && s[t] == ' ') ++t;
if (t) return isNumber(string(s, t, 999));
while (!s.empty() && s.back() == ' ')s.pop_back();
int k = s.find_first_of("Ee");
if (k == string::npos) return isf(s);
else return k != s.size() - 1 && isf(string(s, 0, k)) && isnum(string(s, k + 1, 999));
}
};