Add problem 2055: Plates Between Candles

src/lib.rs

@@ -1427,6 +1427,7 @@ pub mod problem_2042_check_if_numbers_are_ascending_in_a_sentence;
 pub mod problem_2043_simple_bank_system;
 pub mod problem_2047_number_of_valid_words_in_a_sentence;
 pub mod problem_2053_kth_distinct_string_in_an_array;
+pub mod problem_2055_plates_between_candles;
 pub mod problem_2057_smallest_index_with_equal_value;
 pub mod problem_2058_find_the_minimum_and_maximum_number_of_nodes_between_critical_points;
 pub mod problem_2059_minimum_operations_to_convert_number;

src/problem_2055_plates_between_candles/mod.rs

@@ -0,0 +1,27 @@
+pub mod prefix_sum;
+
+pub trait Solution {
+    fn plates_between_candles(s: String, queries: Vec<Vec<i32>>) -> Vec<i32>;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [
+            (("**|**|***|", &[[2, 5], [5, 9]] as &[_]), &[2, 3] as &[_]),
+            (
+                ("***|**|*****|**||**|*", &[[1, 17], [4, 5], [14, 17], [5, 11], [15, 16]]),
+                &[9, 0, 0, 0, 0],
+            ),
+        ];
+
+        for ((s, queries), expected) in test_cases {
+            assert_eq!(
+                S::plates_between_candles(s.to_string(), queries.iter().map(Vec::from).collect()),
+                expected,
+            );
+        }
+    }
+}

src/problem_2055_plates_between_candles/prefix_sum.rs

@@ -0,0 +1,65 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+use std::convert::TryInto;
+
+impl Solution {
+    pub fn plates_between_candles(s: String, queries: Vec<Vec<i32>>) -> Vec<i32> {
+        let mut prefix_sums = vec![(0_u32, 0_u32); s.len()].into_boxed_slice();
+        let mut full_plates = 0;
+        let mut current_plates = 0;
+
+        for (target, c) in prefix_sums.iter_mut().zip(s.bytes()) {
+            if c == b'|' {
+                full_plates += current_plates;
+                current_plates = 0;
+            } else {
+                current_plates += 1;
+            }
+
+            target.1 = full_plates;
+        }
+
+        full_plates += current_plates;
+        current_plates = 0;
+
+        for (target, c) in prefix_sums.iter_mut().zip(s.bytes()).rev() {
+            if c == b'|' {
+                full_plates -= current_plates;
+                current_plates = 0;
+            } else {
+                current_plates += 1;
+            }
+
+            target.0 = full_plates;
+        }
+
+        queries
+            .into_iter()
+            .map(|query| {
+                let [left, right]: [_; 2] = query.try_into().ok().unwrap();
+                let right_sum = prefix_sums[right as u32 as usize].1;
+                let left_sum = prefix_sums[left as u32 as usize].0;
+
+                right_sum.saturating_sub(left_sum) as _
+            })
+            .collect()
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn plates_between_candles(s: String, queries: Vec<Vec<i32>>) -> Vec<i32> {
+        Self::plates_between_candles(s, queries)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}