<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: str) -> int:

        def addSgn(sym, stack):
            if sym == '+':
                val = stack.pop()
                val += stack.pop()
                stack += [val]
                # stack += ['+']
            elif sym == '-':
                if len(stack) >= 2:
                    val = stack.pop()
                    val2 = stack.pop() - val
                    stack += [val2]
                    # stack += ['-']
                else:
                    stack[-1] = -stack[-1]
                    # stack += ['!']


        def createPoliz(s):
            stack = []
            sgn = ''
            flag = False
            j = 0
            for i, sym in enumerate(s):
                if i < j:
                    continue

                if sym == ' ':
                    continue

                if sym == '(':
                    brcnt = 1
                    j = i + 1
                    while brcnt != 0:
                        if s[j] == '(':
                            brcnt += 1
                        if s[j] == ')':
                            brcnt -= 1
                        j += 1
                    else:
                        j -= 1
                    l = len(stack)
                    stack += createPoliz(s[i+1:j])
                    if l == 0 and sgn == '-':
                        stack[-1] = -stack[-1]
                        # stack += ['!']
                    elif sgn != '':
                        addSgn(sgn, stack)
                        sgn = ''

                if (sym >= '0' and sym <= '9'):
                    if (i+1 < len(s) and s[i+1] >= '0' and s[i+1] <= '9'):
                        num = sym
                        j = i + 1
                        while (j < len(s) and s[j] >= '0' and s[j] <= '9'):
                            num += s[j]
                            j += 1
                        sym = num

                    stack += [int(sym)]
                    if sgn != '':
                        addSgn(sgn, stack)
                        sgn = ''
                elif sym == '-' or sym == '+':
                    sgn = sym
                        
            return stack
        

        # def calculatePoliz(stack):
        #     nums = []
        #     while (len(stack) != 0):
        #         sym = stack.pop(0)

        #         if (type(sym) == type(1)):
        #             nums += [sym]

        #         elif sym == '-':
        #             val = nums.pop()
        #             val2 = nums.pop() - val
        #             nums += [val2]

        #         elif sym == '+':
        #             val = nums.pop()
        #             val += nums.pop()
        #             nums += [val]

        #         elif sym == '!':
        #             val = nums.pop()
        #             val = -val
        #             nums += [val]
            
        #     return nums[0]

        return createPoliz(s)[0]

               
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