592. Fraction addition and subtraction

Original link ：592. Fractional addition and subtraction

 

simulation ：
 

class Solution {
public:
    // Find the greatest common divisor by division 
    int gcd(int a, int b) {
        return b ? gcd(b, a % b) : a;
    }
    string fractionAddition(string expression) {
        int n = 0;
        for(auto &x :expression) {
            if(x == '/') n++;
        }
        expression = '+' + expression;
        int a = 0,b = 1,offset = 0;
        int c, d;
        char e;
        for (int i = 0; i < n; i ++ ) {
            sscanf(expression.c_str() + offset, "%c%d/%d", &e, &c, &d);
            offset += (e + to_string(c) + '/' + to_string(d)).size();
            if (e == '-') c = -c;
            int x = a * d + b * c, y = b * d;
            int z = gcd(x, y);
            a = x / z, b = y / z;
        }


        if(b < 0) b = -b, a = -a;
        return to_string(a) + '/' + to_string(b);
    }
};