<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:
        
        #get rid of spaces
        x = [i for i in s if i != ' ']

        #if negative number, combine

        j = 0

        x2 = []

        temp = ''

        while j < len(x):
            if x[j] == '-' and x[j+1] != '(':
                if temp:
                    x2.append(temp)
                    temp = ''
                temp += '-'
            elif x[j] not in ['(','+',')','-', '', ' ']:
                temp += x[j]
            elif x[j] in ['(',')','-']:
                if temp:
                    x2.append(temp)
                    temp = ''
                x2.append(x[j])
            elif temp:
                x2.append(temp)
                temp = ''
            j += 1

        if temp:
            x2.append(temp)

        
        #now all the negatives left come before parantheses
        negstack = []

        neg = 0

        stack = []

        for i in range(len(x2)):
            if x2[i] == ')':
                if negstack:
                    if negstack[-1]:
                        neg -= 1
                    negstack.pop()
            elif x2[i] == '-':
                neg += 1
            elif x2[i] == '(':
                if i != 0  and x2[i-1] == '-':
                    negstack.append(True)
                else:
                    negstack.append(False)
            elif x2[i] not in ['(', '']:
                if neg%2 == 0:
                    stack.append(int(x2[i]))
                else:
                    stack.append(-int(x2[i]))
        
        print(stack)
        return sum(stack)
25259