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3455-minimum-length-of-string-after-operations/README.md

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+<p>You are given a string <code>s</code>.</p>
+
+<p>You can perform the following process on <code>s</code> <strong>any</strong> number of times:</p>
+
+<ul>
+	<li>Choose an index <code>i</code> in the string such that there is <strong>at least</strong> one character to the left of index <code>i</code> that is equal to <code>s[i]</code>, and <strong>at least</strong> one character to the right that is also equal to <code>s[i]</code>.</li>
+	<li>Delete the <strong>closest</strong> character to the <strong>left</strong> of index <code>i</code> that is equal to <code>s[i]</code>.</li>
+	<li>Delete the <strong>closest</strong> character to the <strong>right</strong> of index <code>i</code> that is equal to <code>s[i]</code>.</li>
+</ul>
+
+<p>Return the <strong>minimum</strong> length of the final string <code>s</code> that you can achieve.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<div class="example-block">
+<p><strong>Input:</strong> <span class="example-io">s = &quot;abaacbcbb&quot;</span></p>
+
+<p><strong>Output:</strong> <span class="example-io">5</span></p>
+
+<p><strong>Explanation:</strong><br />
+We do the following operations:</p>
+
+<ul>
+	<li>Choose index 2, then remove the characters at indices 0 and 3. The resulting string is <code>s = &quot;bacbcbb&quot;</code>.</li>
+	<li>Choose index 3, then remove the characters at indices 0 and 5. The resulting string is <code>s = &quot;acbcb&quot;</code>.</li>
+</ul>
+</div>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<div class="example-block">
+<p><strong>Input:</strong> <span class="example-io">s = &quot;aa&quot;</span></p>
+
+<p><strong>Output:</strong> <span class="example-io">2</span></p>
+
+<p><strong>Explanation:</strong><br />
+We cannot perform any operations, so we return the length of the original string.</p>
+</div>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= s.length &lt;= 2 * 10<sup>5</sup></code></li>
+	<li><code>s</code> consists only of lowercase English letters.</li>
+</ul>

3455-minimum-length-of-string-after-operations/solution.py

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+# Approach 1: Using Hash Map
+
+# n = len(s), k = len(character set)
+# Time: O(n)
+# Space: O(k) = O(1)
+
+from collections import Counter
+
+class Solution:
+    def minimumLength(self, s: str) -> int:
+        char_freq = Counter(s)
+
+        delete_count = 0
+
+        for freq in char_freq.values():
+            if freq % 2 == 1:
+                # If frequency is odd, delete all except one
+                delete_count += freq - 1
+            else:
+                # If frequency is even, delete all except two
+                delete_count += freq - 2
+
+        # Return the minimum length after deletions
+        return len(s) - delete_count
+