1776. Car Fleet II: RETRY, credit: https://leetcode.com/problems/car-fleet-ii/solutions/3213685/just-a-runnable-solution/

Author: tan-wei

src/solution/mod.rs

@@ -1339,3 +1339,4 @@ mod s1771_maximize_palindrome_length_from_subsequences;
 mod s1773_count_items_matching_a_rule;
 mod s1774_closest_dessert_cost;
 mod s1775_equal_sum_arrays_with_minimum_number_of_operations;
+mod s1776_car_fleet_ii;

src/solution/s1776_car_fleet_ii.rs

@@ -0,0 +1,93 @@
+/**
+ * [1776] Car Fleet II
+ *
+ * There are n cars traveling at different speeds in the same direction along a one-lane road. You are given an array cars of length n, where cars[i] = [positioni, speedi] represents:
+ *
+ * 	positioni is the distance between the i^th car and the beginning of the road in meters. It is guaranteed that positioni < positioni+1.
+ * 	speedi is the initial speed of the i^th car in meters per second.
+ *
+ * For simplicity, cars can be considered as points moving along the number line. Two cars collide when they occupy the same position. Once a car collides with another car, they unite and form a single car fleet. The cars in the formed fleet will have the same position and the same speed, which is the initial speed of the slowest car in the fleet.
+ * Return an array answer, where answer[i] is the time, in seconds, at which the i^th car collides with the next car, or -1 if the car does not collide with the next car. Answers within 10^-5 of the actual answers are accepted.
+ *  
+ * Example 1:
+ *
+ * Input: cars = [[1,2],[2,1],[4,3],[7,2]]
+ * Output: [1.00000,-1.00000,3.00000,-1.00000]
+ * Explanation: After exactly one second, the first car will collide with the second car, and form a car fleet with speed 1 m/s. After exactly 3 seconds, the third car will collide with the fourth car, and form a car fleet with speed 2 m/s.
+ *
+ * Example 2:
+ *
+ * Input: cars = [[3,4],[5,4],[6,3],[9,1]]
+ * Output: [2.00000,1.00000,1.50000,-1.00000]
+ *
+ *  
+ * Constraints:
+ *
+ * 	1 <= cars.length <= 10^5
+ * 	1 <= positioni, speedi <= 10^6
+ * 	positioni < positioni+1
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.com/problems/car-fleet-ii/
+// discuss: https://leetcode.com/problems/car-fleet-ii/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+impl Solution {
+    // Credit: https://leetcode.com/problems/car-fleet-ii/solutions/3213685/just-a-runnable-solution/
+    pub fn get_collision_times(cars: Vec<Vec<i32>>) -> Vec<f64> {
+        let mut stack: Vec<usize> = Vec::new();
+        let mut result = vec![-1.0; cars.len()];
+
+        for i in (0..cars.len()).rev() {
+            while !stack.is_empty()
+                && (cars[i][1] <= cars[stack[stack.len() - 1]][1]
+                    || (stack.len() > 1
+                        && Self::collision_time(&cars, i, stack[stack.len() - 1])
+                            >= result[stack[stack.len() - 1]]))
+            {
+                stack.pop();
+            }
+            let time = if stack.is_empty() {
+                -1.0
+            } else {
+                Self::collision_time(&cars, i, stack[stack.len() - 1])
+            };
+            result[i] = time;
+            stack.push(i);
+        }
+
+        result
+    }
+
+    pub fn collision_time(cars: &[Vec<i32>], curr: usize, next: usize) -> f64 {
+        (cars[next][0] - cars[curr][0]) as f64 / (cars[curr][1] - cars[next][1]) as f64
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_1776_example_1() {
+        let cars = vec![vec![1, 2], vec![2, 1], vec![4, 3], vec![7, 2]];
+
+        let result = vec![1.00000, -1.00000, 3.00000, -1.00000];
+
+        assert_eq!(Solution::get_collision_times(cars), result);
+    }
+
+    #[test]
+    fn test_1776_example_2() {
+        let cars = vec![vec![3, 4], vec![5, 4], vec![6, 3], vec![9, 1]];
+
+        let result = vec![2.00000, 1.00000, 1.50000, -1.00000];
+
+        assert_eq!(Solution::get_collision_times(cars), result);
+    }
+}