<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(' ', '')
        stack = []
        f_stack = []
        b_stack = []
        num_stack = []
        i = 0
        k = 0
        n = len(s)
        while i < n:
            c = s[i]
            print(i, c, end=' ')
            if c in '0123456789':
                num_stack.append(c)
            elif num_stack:
                num = ''.join(num_stack)
                f_stack.append((k, int(num)))
                num_stack = []
                if b_stack and b_stack[-1][0] == k: # check k is smae level
                    f_stack.append(b_stack.pop())
                    # continue
            if c == '(':
                k += 1
            if c == ')':
                k -= 1
                if b_stack and b_stack[-1][0] == k:
                    f_stack.append(b_stack.pop())
                
            if c in '+':
                b_stack.append((k, c))
            if c in '-':
                if i == 0 or s[i-1] not in '0123456789)':
                    b_stack.append((k, 'n'))
                else:
                    b_stack.append((k, '-'))
            # print(f_stack, b_stack)

            i += 1
            
        if num_stack:
            num = ''.join(num_stack)
            f_stack.append((k, int(num)))
            num_stack = []
            if b_stack and b_stack[-1][0] == k: # check k is smae level
                f_stack.append(b_stack.pop())
        # print(f_stack, b_stack)
        print(list(_[1] for _ in f_stack))
        
        stack = []
        for k, c in f_stack:
            if c == '+':
                n2 = stack.pop()
                n1 = stack.pop()
                stack.append(n1 + n2)
            elif c == '-':
                n2 = stack.pop()
                n1 = stack.pop()
                stack.append(n1 - n2)
            elif c == 'n':
                n1 = stack.pop()
                stack.append(-n1)
            else:
                stack.append(c)

        return stack[0]

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