<p>Given a string <code>s</code> which represents an expression, <em>evaluate this expression and return its value</em>.&nbsp;</p>

<p>The integer division should truncate toward zero.</p>

<p>You may assume that the given expression is always valid. All intermediate results will be in the range of <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>.</p>

<p><strong>Note:</strong> You are not 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 = "3+2*2"
<strong>Output:</strong> 7
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> s = " 3/2 "
<strong>Output:</strong> 1
</pre><p><strong class="example">Example 3:</strong></p>
<pre><strong>Input:</strong> s = " 3+5 / 2 "
<strong>Output:</strong> 5
</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 integers and operators <code>(&#39;+&#39;, &#39;-&#39;, &#39;*&#39;, &#39;/&#39;)</code> separated by some number of spaces.</li>
	<li><code>s</code> represents <strong>a valid expression</strong>.</li>
	<li>All the integers in the expression are non-negative integers in the range <code>[0, 2<sup>31</sup> - 1]</code>.</li>
	<li>The answer is <strong>guaranteed</strong> to fit in a <strong>32-bit integer</strong>.</li>
</ul>

class Solution:

    def handleMultDiv(self, arr: List[str], i: int):
        cur = int(arr[i])
        # print(f"Multiplying starting from index {i}")
        # print(f"i={i}")
        # print(f"not at end: {i+1 < len(arr)}, operation valid: {arr[i+1] == '*' or arr[i+1] == '/'}")
        # print(f"condition matched: {i+i < len(arr) and (arr[i+1] == '*' or arr[i+1] == '/')}")
        # print(f"not at end: {i+1 < len(arr)}, operation valid: {arr[i+1] == '*' or arr[i+1] == '/'}")
        while (i+1 < len(arr)) and (arr[i+1] == '*' or arr[i+1] == '/'):
            i += 1
            operation = arr[i]
            print(f"Operation: {operation}")
            i += 1
            if operation == '*':
                cur *= int(arr[i])
            else:
                cur = int(cur / int(arr[i]))
        print(f"After mult/div, got {cur}, new index: {i}")
        return i+1, int(cur)


    def calculate(self, s: str) -> int:
        # add / subtract from result if next operation is also add or subtract, otherwise handle all multiplications / divisions first
        # parse string in first pass and put each number and operation into a list 
        tokens = []
        curNum = ""
        isNeg = False
        for c in s:
            if c.isdigit():
                curNum += c
            else:
                if len(curNum) > 0:
                    tokens.append(curNum)
                    curNum = ""
                if c == ' ':
                    continue
                else:
                    tokens.append(c)
        if len(curNum) > 0:
            tokens.append(curNum)
        res = 0
        i = 0
        print(tokens)
        while i < len(tokens):
            if i == len(tokens) - 1:
                if isNeg:
                    res -= int(tokens[i])
                else:
                    res += int(tokens[i])
                break
            nextOperation = tokens[i+1]
            if nextOperation == '*' or nextOperation == '/':
                newI, val = self.handleMultDiv(tokens, i)
                print(f"after multiplication, newI={newI}, val = {val}")
                i = newI
            else:
                val = int(tokens[i])
                i += 1
            if isNeg:
                print(f"{res} - {val} = {res - val}")
                res -= val
            else:
                print(f"{res} + {val} = {res + val}")
                res += val
            if i >= len(tokens):
                break
            else:
                isNeg = tokens[i] == '-'
                i += 1
        return int(res)
        
24000