Add problem 2311: Longest Binary Subsequence Less Than or Equal to K

src/lib.rs

@@ -1720,6 +1720,7 @@ pub mod problem_2305_fair_distribution_of_cookies;
 pub mod problem_2306_naming_a_company;
 pub mod problem_2309_greatest_english_letter_in_upper_and_lower_case;
 pub mod problem_2310_sum_of_numbers_with_units_digit_k;
+pub mod problem_2311_longest_binary_subsequence_less_than_or_equal_to_k;
 pub mod problem_2315_count_asterisks;
 pub mod problem_2316_count_unreachable_pairs_of_nodes_in_an_undirected_graph;
 pub mod problem_2317_maximum_xor_after_operations;

src/problem_2311_longest_binary_subsequence_less_than_or_equal_to_k/greedy.rs

@@ -0,0 +1,38 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    pub fn longest_subsequence(s: String, k: i32) -> i32 {
+        let s = s.as_bytes();
+        let n = s.len();
+        let k = k as u32;
+        let bits = 32 - k.leading_zeros() as usize;
+
+        if n < bits {
+            return n as _;
+        }
+
+        let (left, right) = s.split_at(n - bits);
+        let right = right.iter().fold(0, |right, &c| (right << 1) + u32::from(c & 1));
+        let length = bits as u16 - u16::from(right > k);
+
+        i32::from(left.iter().fold(length, |length, &c| length + u16::from(b'1' - c)))
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn longest_subsequence(s: String, k: i32) -> i32 {
+        Self::longest_subsequence(s, k)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_2311_longest_binary_subsequence_less_than_or_equal_to_k/mod.rs

@@ -0,0 +1,29 @@
+pub mod greedy;
+
+pub trait Solution {
+    fn longest_subsequence(s: String, k: i32) -> i32;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [
+            (("1001010", 5), 5),
+            (("00101001", 1), 6),
+            (
+                (
+                    "101100011000010101011100011111111001011101000101000010001100101110010010011000100010001110011111000100100101110000100010010010100010",
+                    978_095_074,
+                ),
+                84,
+            ),
+            (("0", 583_196_182), 1),
+        ];
+
+        for ((s, k), expected) in test_cases {
+            assert_eq!(S::longest_subsequence(s.to_string(), k), expected);
+        }
+    }
+}