<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>

from typing import Callable
from re import Pattern

class Solution:
    def calculate(self, s: str) -> int:
        return self._calculate_part(
            s,
            operators_list=[
                r"[+-]",
                r"[\*/]",
            ],
            operator_dicts=[
                {
                    "+": lambda left, right: left + right,
                    "-": lambda left, right: left - right,
                },
                {
                    "*": lambda left, right: left * right,
                    "/": lambda left, right: left // right,
                },
            ]
        )
    
    def _calculate_part(self, part: str, operators_list: list[Pattern], operator_dicts: list[dict[str, Callable[[int, int], int]]]) -> int:
        import re

        if not operators_list:
            return int(part)

        parts = re.split(operators_list[0], part)
        left = self._calculate_part(parts[0], operators_list[1:], operator_dicts[1:])
        s_i = len(parts[0])
        for i in range(1, len(parts)):
            operator = part[s_i]
            right = parts[i]
            right = self._calculate_part(parts[i], operators_list[1:], operator_dicts[1:])
            left = operator_dicts[0][operator](left, right)
            s_i += 1 + len(parts[i])
        return left
        
19600