leetcode

0 class Solution {

1 using it_t = string::const_iterator;

2

3 static bool validSign(it_t &pos, const it_t &end) {

4 if (*pos == '-' || *pos == '+') {

5 pos++;

6 if (find(pos, end, '-') != end || find(pos, end, '+') != end) {

7 return false;

8 }

9 }

10

11 return pos != end;

12 }

13

14 static bool validDigit(const it_t &pos, const it_t &end) {

15 return all_of(pos, end, [](char c) { return isdigit(c); });

16 }

17

18 static bool isDecimal(const string &s) {

19 auto pos = begin(s);

20

21 if (!validSign(pos, end(s))) return false;

22 if (string(pos, end(s)) == ".") return false;

23

24 auto dot = find(pos, end(s), '.');

25 return validDigit(pos, dot) && validDigit(dot + 1, end(s));

26 }

27

28 static bool isInteger(const string &s) {

29 auto pos = begin(s);

30 if (!validSign(pos, end(s))) return false;

31 return validDigit(pos, end(s));

32 }

33

34 public:

35 bool isNumber(const string &s) const {

36 auto e = s.find('e'), E = s.find('E');

37

38 if (E != string::npos) swap(e, E);

39 if (e != string::npos) {

40 const string first = s.substr(0, e);

41 const string second = s.substr(e + 1);

42 return !first.empty() && !second.empty() && isInteger(second) &&

43 (isDecimal(first) || isInteger(first));

44 }

45

46 return isDecimal(s) || isInteger(s);

47 }

48 };