592.cpp

// gcd+lcm.cpp
class Solution {
public:
  string fractionAddition(string expression) {
    stringstream ss(expression);
    int a, b, suma = 0, sumb = 1;
    char ch;
    while (ss >> a >> ch >> b) {
      int _lcm = lcm(b, sumb);
      suma *= _lcm / sumb;
      sumb = _lcm;
      a *= _lcm / b;
      suma += a;
      int _gcd = gcd(suma, sumb);
      suma /= _gcd;
      sumb /= _gcd;
    }
    if (suma * sumb < 0)
      return "-" + to_string(abs(suma)) + "/" + to_string(abs(sumb));
    return to_string(abs(suma)) + "/" + to_string(abs(sumb));
  }
  int gcd(int a, int b) {
    if (a < b)
      return gcd(b, a);
    int temp;
    while (b != 0) {
      temp = a % b;
      a = b;
      b = temp;
    }
    return a;
  }
  int lcm(int a, int b) { return a * b / gcd(a, b); }
};