baseball_solution.cpp

bool is_number(const std::string& op);

class Solution {
public:
    int calPoints(vector<string>& ops) {
        std::vector<int> nums;
        for (std::size_t i{}; i < ops.size(); ++i)
        {
            if (is_number(ops[i]))
            {
                // record a new score
                nums.push_back(std::stoi(ops[i]));
            }
            else
            {
                if (ops[i] == "+")
                {
                    // record a new score that is the sum of the previous two scores 
                    // it is guaranteed there will always be two previous scores
                    int sum{nums[nums.size() - 1] + nums[nums.size() - 2]};
                    nums.push_back(sum);
                }
                else if (ops[i] == "D")
                {
                    // record a new score that is double the previous score
                    // it is guaranteed there will always be a previous score
                    int doubled{nums[nums.size() - 1] * 2};
                    nums.push_back(doubled);
                }
                else if (ops[i] == "C")
                {
                    // invalidate the previous score, removing it from the record
                    // it is guaranteed there will always be a previous score
                    nums.pop_back();
                }
            }
        }
        
        return std::accumulate(nums.begin(), nums.end(), 0);
    }
};

bool is_number(const std::string& op)
{
    // first check if number starts with a sign character
    char sign = ' ';
    bool flag = false; // to check for digits
    if (op[0] == '-' || op[0] == '+')
    {
        sign = op[0];
        for (std::size_t i{1}; i < op.length(); ++i)
        {
            if (std::isdigit(op[i]))
            {
                flag = true;
            }
            else
            {
                flag = false;
            }
        }
    }
    else
    {
        for (std::size_t i{}; i < op.length(); ++i)
        {
            if (std::isdigit(op[i]))
            {
                flag = true;
            }
            else
            {
                flag = false;
            }
        }
    }
    return flag;
}