<p>Given an arithmetic equation consisting of positive integers, +, -, * and / (no paren­theses), compute the result.</p> <p>The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division should truncate toward zero.</p> <p><strong>Example 1:</strong></p> <pre> <strong>Input: </strong>"3+2*2" <strong>Output:</strong> 7 </pre> <p><strong>Example 2:</strong></p> <pre> <strong>Input:</strong> " 3/2 " <strong>Output:</strong> 1</pre> <p><strong>Example 3:</strong></p> <pre> <strong>Input:</strong> " 3+5 / 2 " <strong>Output:</strong> 5 </pre> <p><strong>Note:</strong></p> <ul> <li>You may assume that the given expression is always valid.</li> <li>Do not use the eval built-in library function.</li> </ul>