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Java-based LeetCode algorithm problem solutions, regularly updated

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679\. 24 Game

Hard

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

You are restricted with the following rules:

*   The division operator `'/'` represents real division, not integer division.
    *   For example, `4 / (1 - 2 / 3) = 4 / (1 / 3) = 12`.
*   Every operation done is between two numbers. In particular, we cannot use `'-'` as a unary operator.
    *   For example, if `cards = [1, 1, 1, 1]`, the expression `"-1 - 1 - 1 - 1"` is **not allowed**.
*   You cannot concatenate numbers together
    *   For example, if `cards = [1, 2, 1, 2]`, the expression `"12 + 12"` is not valid.

Return `true` if you can get such expression that evaluates to `24`, and `false` otherwise.

**Example 1:**

**Input:** cards = [4,1,8,7]

**Output:** true

**Explanation:** (8-4) \* (7-1) = 24

**Example 2:**

**Input:** cards = [1,2,1,2]

**Output:** false

**Constraints:**

*   `cards.length == 4`
*   `1 <= cards[i] <= 9`