<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:
        s = s.replace(" ", "")
        last_digit = ""
        all_elements = list()
        for element in s:
            if element in ['+', '-', '(', ')']:
                if last_digit != "":
                    all_elements.append(last_digit)
                    last_digit = ""
                all_elements.append(element)
            else:
                last_digit += element
        if last_digit != "":
            all_elements.append(last_digit)
        print(all_elements)

        stack = list()
        for element in all_elements:
            if element == ')':
                reversed_list = list()
                while True:
                    reversed_list.append(stack.pop())
                    if reversed_list[-1] == '(':
                        break
                used_list = reversed_list[:-1][::-1]
                operators = [""]
                for item in used_list:
                    if item in ["+", "-"]:
                        if operators == [""]:
                            operators[-1] = 0
                        else:
                            operators[-1] = int(operators[-1])
                        operators.append(item)
                        operators.append("")
                    elif type(item) == int:
                        # precomputed val
                        operators[-1] = item
                    else:
                        operators[-1] += item
                operators[-1] = int(operators[-1])
                val = operators[0]
                i = 1
                while i < len(operators):
                    if operators[i] == "+":
                        val += operators[i+1]
                        i += 2
                    elif operators[i] == "-":
                        val -= operators[i+1]
                        i += 2
                    else:
                        i += 1
                stack.append(val)
            else:
                stack.append(element)
        operators = [""]
        for element in stack:
            if element in ["+", "-"]:
                if operators == [""]:
                    operators[-1] = 0
                else:
                    operators[-1] = int(operators[-1])
                operators.append(element)
                operators.append("")
            elif type(element) == int:
                operators[-1] = element
            else:
                operators[-1] += element
        index = 1
        vals = int(operators[0])
        while index<len(operators):
            if operators[index] == '+':
                vals += int(operators[index+1])
                index += 2
            elif operators[index] == '-':
                vals -= int(operators[index+1])
                index += 2
            else:
                index += 1

        return vals

        
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