Sync LeetCode submission Runtime - 5 ms (39.84%), Memory - 17.9 MB (47.97%)

Author: jimit105

2395-longest-binary-subsequence-less-than-or-equal-to-k/README.md

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+<p>You are given a binary string <code>s</code> and a positive integer <code>k</code>.</p>
+
+<p>Return <em>the length of the <strong>longest</strong> subsequence of </em><code>s</code><em> that makes up a <strong>binary</strong> number less than or equal to</em> <code>k</code>.</p>
+
+<p>Note:</p>
+
+<ul>
+	<li>The subsequence can contain <strong>leading zeroes</strong>.</li>
+	<li>The empty string is considered to be equal to <code>0</code>.</li>
+	<li>A <strong>subsequence</strong> is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters.</li>
+</ul>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;1001010&quot;, k = 5
+<strong>Output:</strong> 5
+<strong>Explanation:</strong> The longest subsequence of s that makes up a binary number less than or equal to 5 is &quot;00010&quot;, as this number is equal to 2 in decimal.
+Note that &quot;00100&quot; and &quot;00101&quot; are also possible, which are equal to 4 and 5 in decimal, respectively.
+The length of this subsequence is 5, so 5 is returned.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;00101001&quot;, k = 1
+<strong>Output:</strong> 6
+<strong>Explanation:</strong> &quot;000001&quot; is the longest subsequence of s that makes up a binary number less than or equal to 1, as this number is equal to 1 in decimal.
+The length of this subsequence is 6, so 6 is returned.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= s.length &lt;= 1000</code></li>
+	<li><code>s[i]</code> is either <code>&#39;0&#39;</code> or <code>&#39;1&#39;</code>.</li>
+	<li><code>1 &lt;= k &lt;= 10<sup>9</sup></code></li>
+</ul>

2395-longest-binary-subsequence-less-than-or-equal-to-k/solution.py

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+# Approach: Greedy
+
+# Time: O(n)
+# Space: O(1)
+
+class Solution:
+    def longestSubsequence(self, s: str, k: int) -> int:
+        sm = 0
+        cnt = 0
+        bits = k.bit_length()
+
+        for i, ch in enumerate(s[::-1]):
+            if ch == '1':
+                if i < bits and sm + (1 << i) <= k:
+                    sm += 1 << i
+                    cnt += 1
+            else:
+                cnt += 1
+
+        return cnt
+