# Problem Definition

## Description

Evaluate the value of an arithmetic expression in [Reverse Polish Notation](http://en.wikipedia.org/wiki/Reverse_Polish_notation).

Valid operators are `+`, `-`, `*`, `/`. Each operand may be an integer or another expression.

**Note:**

* Division between two integers should truncate toward zero.
* The given RPN expression is always valid. That means the expression would always evaluate to a result and there won't be any divide by zero operation.

**Example 1:**

```plaintext
Input: ["2", "1", "+", "3", "*"]
Output: 9
Explanation: ((2 + 1) * 3) = 9
```

**Example 2:**

```plaintext
Input: ["4", "13", "5", "/", "+"]
Output: 6
Explanation: (4 + (13 / 5)) = 6
```

**Example 3:**

```plaintext
Input: ["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"]
Output: 22
Explanation:
  ((10 * (6 / ((9 + 3) * -11))) + 17) + 5
= ((10 * (6 / (12 * -11))) + 17) + 5
= ((10 * (6 / -132)) + 17) + 5
= ((10 * 0) + 17) + 5
= (0 + 17) + 5
= 17 + 5
= 22
```

## Notes

1. [ProgramCreek](https://www.programcreek.com/2012/12/leetcode-evaluate-reverse-polish-notation/)
1. [LeetCode discussion - [Java] Accepted Code: Stack implementation.](https://leetcode.com/explore/interview/card/google/63/sorting-and-searching-4/468/discuss/47430/Java-Accepted-Code:-Stack-implementation.)