Add problem 2211: Count Collisions on a Road

src/lib.rs

@@ -1650,6 +1650,7 @@ pub mod problem_2207_maximize_number_of_subsequences_in_a_string;
 pub mod problem_2208_minimum_operations_to_halve_array_sum;
 pub mod problem_2209_minimum_white_tiles_after_covering_with_carpets;
 pub mod problem_2210_count_hills_and_valleys_in_an_array;
+pub mod problem_2211_count_collisions_on_a_road;
 pub mod problem_2215_find_the_difference_of_two_arrays;
 pub mod problem_2216_minimum_deletions_to_make_array_beautiful;
 pub mod problem_2218_maximum_value_of_k_coins_from_piles;

src/problem_2211_count_collisions_on_a_road/iterative.rs

@@ -0,0 +1,79 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+enum State {
+    AllLeft,
+    Stop,
+    Right(u32),
+}
+
+impl Solution {
+    pub fn count_collisions(directions: String) -> i32 {
+        let mut result = 0;
+        let mut state = State::AllLeft;
+        let mut iter = directions.bytes();
+
+        loop {
+            match state {
+                State::AllLeft => {
+                    if let Some(c) = iter.next() {
+                        match c {
+                            b'L' => {}
+                            b'R' => state = State::Right(1),
+                            _ => state = State::Stop,
+                        }
+                    } else {
+                        break;
+                    }
+                }
+                State::Stop => {
+                    if let Some(c) = iter.next() {
+                        match c {
+                            b'L' => result += 1,
+                            b'R' => state = State::Right(1),
+                            _ => {}
+                        }
+                    } else {
+                        break;
+                    }
+                }
+                State::Right(count) => {
+                    if let Some(c) = iter.next() {
+                        match c {
+                            b'L' => {
+                                result += count + 1;
+                                state = State::Stop;
+                            }
+                            b'R' => state = State::Right(count + 1),
+                            _ => {
+                                result += count;
+                                state = State::Stop;
+                            }
+                        }
+                    } else {
+                        break;
+                    }
+                }
+            }
+        }
+
+        result as _
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn count_collisions(directions: String) -> i32 {
+        Self::count_collisions(directions)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_2211_count_collisions_on_a_road/iterative_2.rs

@@ -0,0 +1,32 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    pub fn count_collisions(directions: String) -> i32 {
+        let directions = directions.into_bytes();
+        let left = directions.iter().take_while(|&&c| c == b'L').count();
+        let right = directions.iter().rev().take_while(|&&c| c == b'R').count();
+
+        directions[left..directions.len() - right]
+            .iter()
+            .filter(|&&c| c != b'S')
+            .count() as _
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn count_collisions(directions: String) -> i32 {
+        Self::count_collisions(directions)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_2211_count_collisions_on_a_road/mod.rs

@@ -0,0 +1,19 @@
+pub mod iterative;
+pub mod iterative_2;
+
+pub trait Solution {
+    fn count_collisions(directions: String) -> i32;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [("RLRSLL", 5), ("LLRR", 0), ("LLSRSSRSSLLSLLLRSLSRL", 11), ("L", 0)];
+
+        for (directions, expected) in test_cases {
+            assert_eq!(S::count_collisions(directions.to_string()), expected);
+        }
+    }
+}