Sync LeetCode submission Runtime - 58 ms (25.91%), Memory - 17.7 MB (96.09%)

Author: jimit105

1160-letter-tile-possibilities/README.md

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+<p>You have <code>n</code>&nbsp;&nbsp;<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>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> tiles = &quot;AAB&quot;
+<strong>Output:</strong> 8
+<strong>Explanation: </strong>The possible sequences are &quot;A&quot;, &quot;B&quot;, &quot;AA&quot;, &quot;AB&quot;, &quot;BA&quot;, &quot;AAB&quot;, &quot;ABA&quot;, &quot;BAA&quot;.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> tiles = &quot;AAABBC&quot;
+<strong>Output:</strong> 188
+</pre>
+
+<p><strong class="example">Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> tiles = &quot;V&quot;
+<strong>Output:</strong> 1
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= tiles.length &lt;= 7</code></li>
+	<li><code>tiles</code> consists of uppercase English letters.</li>
+</ul>

1160-letter-tile-possibilities/solution.py

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+# Approach 2: Optimized Recursion
+
+# Time: O(2^n)
+# Space: O(n)
+
+class Solution:
+    def numTilePossibilities(self, tiles: str) -> int:
+        char_count = [0] * 26
+        for char in tiles:
+            char_count[ord(char) - ord('A')] += 1
+
+        return self._find_sequences(char_count)
+
+    def _find_sequences(self, char_count):
+        total = 0
+
+        for pos in range(26):
+            if char_count[pos] == 0:
+                continue
+
+            # Add current char and recurse
+            total += 1
+            char_count[pos] -= 1
+            total += self._find_sequences(char_count)
+            char_count[pos] += 1
+
+        return total
+