코테준비 - Valid Number

Valid Number

class Solution {
public:
  bool signSideValidation(int idx, const string &s){
      if(s.length() == 1) return false;
      char right;
      char left;
      if (idx == 0) {
          right = s.at(idx + 1);
          if (right == '.' || (right >= '0' && right <= '9')) return true;
      } else if (idx == s.length() - 1) {
          return false;
      } else {
          left = s.at(idx - 1);
          if(left == 'e' || left == 'E') return true;
      }

      return false;
  }

  bool dotSideValidation(int idx, const string &s) {
      if (s.length() == 1) return false;
      char right;
      char left;
      if (idx == 0) {
          right = s.at(idx + 1);
          if (right >= '0' && right <= '9') return true;
      } else if (idx == s.length() - 1) {
          left = s.at(idx - 1);
          if (left >= '0' && left <= '9') return true;
      } else {
          right = s.at(idx + 1);
          left = s.at(idx - 1);
          if ((right >= '0' && right <= '9') || (left >= '0' && left <= '9')) return true;
      }

      return false;
  }

  bool isNumber(string s) {
      bool decimal = true;
      bool decimalSign = false;
      bool integer = false;
      bool integerSign = false;
      bool dot = false;

      int idx = 0;
      for (auto &c: s) {
          switch (c) {
              case '-':
              case '+':
                  if (idx == s.length() - 1 || !signSideValidation(idx, s))
                      return false;
                  if (s.length() == 1 || decimal) {
                      if (decimalSign || idx != 0) return false;
                      decimalSign = true;
                  } else {
                      if (integerSign || (s.at(idx - 1) != 'e' && s.at(idx - 1) != 'E')) return false;
                      integerSign = true;
                  }
                  break;
              case 'e':
              case 'E':
                  if (idx == s.length() - 1 || idx == 0 || integer) return false;
                  decimal = false;
                  integer = true;
                  break;
              case '.':
                  if (!dotSideValidation(idx, s)) return false;
                  if (s.length() == 1 || integer || dot) return false;
                  dot = true;
                  break;
              default:
                  if (c < '0' || c > '9') return false;
                  break;
          }
          idx++;
      }
      return true;
  }
};