<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:
    def calculate(self, s):
        # prepare data
        convertedS = []
        par = ''

        def addPar(par):
            if par != '':
                convertedS.append(int(par))
            return ''
            

        def isDigit(val):
            return i in '1234567890'

        for i in s:
            if i == ' ':
                par = addPar(par)
                continue
            if isDigit(i):
                par += i
            else:
                par = addPar(par)
                convertedS.append(i)
        if par:
            convertedS.append(int(par))

        def solveBrackets(poz):
            s = 0
            isNeg = False
            idx = poz + 1

            while idx < size:
                i = convertedS[idx]
                if i == '-':
                    isNeg = True
                elif i == '+':
                    isNeg = False
                elif i == '(':
                    res = solveBrackets(idx)
                    if not isNeg:
                        s += res[0]
                    else:
                        s -= res[0]
                    idx = res[1]
                    isNeg = False
                elif i == ')':
                    return s,idx
                else:
                    if isNeg:
                        s -= i
                    else:
                        s += i
                    isNeg = False
                idx += 1

        convertedS = ['('] + convertedS + [')']
        size = len(convertedS)
        return solveBrackets(0)[0]

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