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65-Valid-Number.cpp
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65-Valid-Number.cpp
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class Solution {
public:
bool isNumber(string s) {
s = trim(s);
if (s.empty()) return false;
return parse(s);
}
bool parse(string &s) {
int idx = 0;
if (!parseFloat(s, idx)) return false;
if (idx >= s.size()) return true;
if (s[idx] == 'e') {
idx++;
if (idx >= s.size()) return false;
if (!parseInt(s, idx)) return false;
}
return idx >= s.size();
}
bool parseFloat(string &s, int &idx) {
if (idx >= s.size()) return false;
if (s[idx] == '-' || s[idx] == '+') idx++;
if (idx >= s.size()) return false;
if (s[idx] == '.') return parseNumeric(s, ++idx);
if (!parseNumeric(s, idx)) return false;
if (idx >= s.size()) return true;
if (s[idx] == '.') parseNumeric(s, ++idx);
return true;
}
bool parseInt(string &s, int &idx) {
if (idx >= s.size()) return false;
if (s[idx] == '-' || s[idx] == '+') idx++;
if (idx >= s.size()) return false;
return parseNumeric(s, idx);
}
bool parseNumeric(string &s, int &idx) {
int i = idx;
while (idx < s.size() && isnumeric(s[idx])) idx++;
return idx != i;
}
bool isnumeric(char c) {
return '0' <= c && c <= '9';
}
string& trim(string &s) {
if (s.empty())
return s;
s.erase(0, s.find_first_not_of(" "));
s.erase(s.find_last_not_of(" ") + 1);
return s;
}
};