<p>Given a string <code>s</code> representing a valid expression, implement a basic calculator to evaluate it, and return <em>the result of the evaluation</em>.</p>

<p><strong>Note:</strong> You are <strong>not</strong> allowed to use any built-in function which evaluates strings as mathematical expressions, such as <code>eval()</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;1 + 1&quot;
<strong>Output:</strong> 2
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot; 2-1 + 2 &quot;
<strong>Output:</strong> 3
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;(1+(4+5+2)-3)+(6+8)&quot;
<strong>Output:</strong> 23
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 3 * 10<sup>5</sup></code></li>
	<li><code>s</code> consists of digits, <code>&#39;+&#39;</code>, <code>&#39;-&#39;</code>, <code>&#39;(&#39;</code>, <code>&#39;)&#39;</code>, and <code>&#39; &#39;</code>.</li>
	<li><code>s</code> represents a valid expression.</li>
	<li><code>&#39;+&#39;</code> is <strong>not</strong> used as a unary operation (i.e., <code>&quot;+1&quot;</code> and <code>&quot;+(2 + 3)&quot;</code> is invalid).</li>
	<li><code>&#39;-&#39;</code> could be used as a unary operation (i.e., <code>&quot;-1&quot;</code> and <code>&quot;-(2 + 3)&quot;</code> is valid).</li>
	<li>There will be no two consecutive operators in the input.</li>
	<li>Every number and running calculation will fit in a signed 32-bit integer.</li>
</ul>

class Solution {
public:
    std::string evaluateString(string s)
    {
        std::vector<std::string> equation;
        int res = 0;
        int start = 0;

        for (int i = start; i < s.size(); ++i)
        {
            if (s[i] == '+' || s[i] == '-' || s[i] == '*' || s[i] == '/')
            {
                if (i == 0)
                {
                    if (s[i] == '-' && s[i+1] == '-')
                    {
                        start = 2;
                        ++i;
                    }
                    continue;
                }
                if (s[i] == '-' && s[i+1] == '-')
                {
                    equation.push_back(s.substr(start, i - start));
                    equation.push_back("+");
                    start = i + 2;
                    ++i;
                    continue;
                }
                else if (s[i] == '+' && s[i+1] == '-')
                {
                    equation.push_back(s.substr(start, i - start));
                    equation.push_back("-");
                    start = i + 2;
                    ++i;
                    continue;
                }
                else if (s[i] == '*' && s[i+1] == '-')
                {
                    equation.push_back("-1");
                    equation.push_back("*");
                    equation.push_back(s.substr(start, i - start));
                    equation.push_back("*");
                    start = i + 2;
                    ++i;
                    continue;
                }
                else if (s[i] == '*' && s[i+1] == '/')
                {
                    equation.push_back("-1");
                    equation.push_back("*");
                    equation.push_back(s.substr(start, i - start));
                    equation.push_back("/");
                    start = i + 2;
                    ++i;
                    continue;
                }
                equation.push_back(s.substr(start, i - start));
                equation.push_back(s.substr(i, 1));
                start = i + 1;
                continue;
            }
            if (i == s.size() - 1)
            {
                equation.push_back(s.substr(start, i - start + 1));
            }
        }

        bool multiAndDivDone = false;

        while (equation.size() > 1)
        {
            if(!multiAndDivDone)
            {
                for (int i = 0; i < equation.size() - 1; ++i)
                {
                    if(equation[i] == "*")
                    {
                        equation[i-1] = std::to_string(std::stoi(equation[i-1]) * std::stoi(equation[i+1]));
                        equation.erase(equation.begin() + i, equation.begin() + i + 2);
                        break;
                    }
                    if(equation[i] == "/")
                    {
                        equation[i-1] = std::to_string(std::stoi(equation[i-1]) / std::stoi(equation[i+1]));
                        equation.erase(equation.begin() + i, equation.begin() + i + 2);
                        break;
                    }
                }
                multiAndDivDone = true;
            }


            for (int i = 0; i < equation.size() - 1; ++i)
            {
                if(equation[i] == "+")
                {
                    equation[i-1] = std::to_string(std::stoi(equation[i-1]) + std::stoi(equation[i+1]));
                    equation.erase(equation.begin() + i, equation.begin() + i + 2);
                    break;
                }
                if(equation[i] == "-")
                {
                    equation[i-1] = std::to_string(std::stoi(equation[i-1]) - std::stoi(equation[i+1]));
                    equation.erase(equation.begin() + i, equation.begin() + i + 2);
                    break;
                }
            }
        }

        return equation[0];//std::stoi(equation[0]);
    }


    int calculate(string s) {
        s.erase(std::remove_if(s.begin(), s.end(), [](char x){return std::isspace(x);}), s.end());
        int j = 1;

        while (true)
        {
            int bracket_start = -1;

            for (int i = 0; i < s.length(); ++i)
            {
                if (s[i] == '(') bracket_start = i;
                else if (s[i] == ')')
                {
                    std::string result = evaluateString(s.substr(bracket_start + 1, i - bracket_start - 1));
                  
                    s.replace(bracket_start, i - bracket_start + 1, result);

                    break;
                }
            }
            if (bracket_start == -1) return std::stoi(evaluateString(s));
        }

        return -1;
    }
};
39368