<p>You are given an integer array <code>cards</code> of length <code>4</code>. You have four cards, each containing a number in the range <code>[1, 9]</code>. You should arrange the numbers on these cards in a mathematical expression using the operators <code>[&#39;+&#39;, &#39;-&#39;, &#39;*&#39;, &#39;/&#39;]</code> and the parentheses <code>&#39;(&#39;</code> and <code>&#39;)&#39;</code> to get the value 24.</p>

<p>You are restricted with the following rules:</p>

<ul>
	<li>The division operator <code>&#39;/&#39;</code> represents real division, not integer division.

	<ul>
		<li>For example, <code>4 / (1 - 2 / 3) = 4 / (1 / 3) = 12</code>.</li>
	</ul>
	</li>
	<li>Every operation done is between two numbers. In particular, we cannot use <code>&#39;-&#39;</code> as a unary operator.
	<ul>
		<li>For example, if <code>cards = [1, 1, 1, 1]</code>, the expression <code>&quot;-1 - 1 - 1 - 1&quot;</code> is <strong>not allowed</strong>.</li>
	</ul>
	</li>
	<li>You cannot concatenate numbers together
	<ul>
		<li>For example, if <code>cards = [1, 2, 1, 2]</code>, the expression <code>&quot;12 + 12&quot;</code> is not valid.</li>
	</ul>
	</li>
</ul>

<p>Return <code>true</code> if you can get such expression that evaluates to <code>24</code>, and <code>false</code> otherwise.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> cards = [4,1,8,7]
<strong>Output:</strong> true
<strong>Explanation:</strong> (8-4) * (7-1) = 24
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> cards = [1,2,1,2]
<strong>Output:</strong> false
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>cards.length == 4</code></li>
	<li><code>1 &lt;= cards[i] &lt;= 9</code></li>
</ul>

from itertools import product, permutations

class Solution:
    def eval_postfix(self, expr: List):
        stack = []
        for token in expr:
            if token not in {'+','-', '*', '/'}:
                stack.append(token)
            else:
                if token == '+':
                    new_val = stack[-2] + stack[-1]
                elif token == '-':
                    new_val = stack[-2] - stack[-1]
                elif token == '*':
                    new_val = stack[-2] * stack[-1]
                else:
                    new_val = (stack[-2] / stack[-1]) if stack[-1] != 0.0 else float('nan')

                del stack[-1]
                del stack[-1]
                stack.append(new_val)

        return round(stack[-1], 6)

    def judgePoint24(self, cards: List[int]) -> bool:
        for ops in product('+-*/', repeat=3):
            for cards_p in permutations(cards, 4):
                a,b,c,d = cards_p
                exprs = [
                    [a, b, ops[0], c, ops[1], d, ops[2]],
                    [a, b, ops[0], c, d, ops[1], ops[2]],
                    [a, b, c, ops[0], d, ops[1], ops[2]],
                    [a, b, c, d, ops[0], ops[1], ops[2]],
                ]
                for expr in exprs:
                    result = self.eval_postfix(expr)
                    if abs(result - 24) <= 1:
                        print(expr, result)

                    if result == 24.0:
                        return True
        return False
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