<p>You have <code>n</code> <code>tiles</code>, where each tile has one letter <code>tiles[i]</code> printed on it.</p> <p>Return <em>the number of possible non-empty sequences of letters</em> you can make using the letters printed on those <code>tiles</code>.</p> <p> </p> <p><strong>Example 1:</strong></p> <pre> <strong>Input:</strong> tiles = "AAB" <strong>Output:</strong> 8 <strong>Explanation: </strong>The possible sequences are "A", "B", "AA", "AB", "BA", "AAB", "ABA", "BAA". </pre> <p><strong>Example 2:</strong></p> <pre> <strong>Input:</strong> tiles = "AAABBC" <strong>Output:</strong> 188 </pre> <p><strong>Example 3:</strong></p> <pre> <strong>Input:</strong> tiles = "V" <strong>Output:</strong> 1 </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= tiles.length <= 7</code></li> <li><code>tiles</code> consists of uppercase English letters.</li> </ul>