Leet Code Daily 2024-07-14 - Number of Atoms

class Formula {

public:
    static shared_ptr<Formula> empty() { return make_shared<Formula>(); }

    static shared_ptr<Formula> of(string name) {
        auto ptr = make_shared<Formula>();
        ptr->count[name] = 1;
        return ptr;
    }

    string toString() {
        string ret = "";
        for (const auto& pair : this->count) {
            ret.append(pair.first);
            if (pair.second > 1) {
                ret.append(to_string(pair.second));
            }
        }
        return ret;
    }

    void add(const shared_ptr<Formula> other) {
        for (const auto& pair : other->count) {
            this->count[pair.first] += pair.second;
        }
    }

    void times(int value) {
        for (auto& pair : this->count) {
            pair.second *= value;
        }
    }

private:
    map<string, int> count;
};

class Solution {
public:
    string countOfAtoms(string formula) {
        formula = "(" + formula + ")";
        stack<optional<shared_ptr<Formula>>> stack;
        for (int i = 0; i < formula.size(); i++) {
            if (formula[i] == '(') {
                stack.push(nullopt);
                continue;
            }
            if (formula[i] == ')') {
                auto res = Formula::empty();
                for (; stack.top().has_value(); stack.pop()) {
                    res->add(stack.top().value());
                }
                stack.top() = res;
                continue;
            }
            if (isalpha(formula[i])) {
                string name(1, formula[i]);
                while (i + 1 < formula.size() && islower(formula[i + 1])) {
                    name.push_back(formula[++i]);
                }
                stack.push(Formula::of(name));
                continue;
            }
            if (isdigit(formula[i])) {
                int times = formula[i] - '0';
                while (i + 1 < formula.size() && isdigit(formula[i + 1])) {
                    times = 10 * times + (formula[++i] - '0');
                }
                stack.top().value()->times(times);
            }
        }
        return stack.top().value()->toString();
    }
};