<p>Evaluate the value of an arithmetic expression in <a href="http://en.wikipedia.org/wiki/Reverse_Polish_notation" target="_blank">Reverse Polish Notation</a>.</p> <p>Valid operators are <code>+</code>, <code>-</code>, <code>*</code>, and <code>/</code>. Each operand may be an integer or another expression.</p> <p><strong>Note</strong> that division between two integers should truncate toward zero.</p> <p>It is guaranteed that the given RPN expression is always valid. That means the expression would always evaluate to a result, and there will not be any division by zero operation.</p> <p> </p> <p><strong>Example 1:</strong></p> <pre> <strong>Input:</strong> tokens = ["2","1","+","3","*"] <strong>Output:</strong> 9 <strong>Explanation:</strong> ((2 + 1) * 3) = 9 </pre> <p><strong>Example 2:</strong></p> <pre> <strong>Input:</strong> tokens = ["4","13","5","/","+"] <strong>Output:</strong> 6 <strong>Explanation:</strong> (4 + (13 / 5)) = 6 </pre> <p><strong>Example 3:</strong></p> <pre> <strong>Input:</strong> tokens = ["10","6","9","3","+","-11","*","/","*","17","+","5","+"] <strong>Output:</strong> 22 <strong>Explanation:</strong> ((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 </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= tokens.length <= 10<sup>4</sup></code></li> <li><code>tokens[i]</code> is either an operator: <code>"+"</code>, <code>"-"</code>, <code>"*"</code>, or <code>"/"</code>, or an integer in the range <code>[-200, 200]</code>.</li> </ul>