Package g2201_2300.s2211_count_collisions_on_a_road

Class Solution

java.lang.Object
g2201_2300.s2211_count_collisions_on_a_road.Solution
public class Solution extends Object
2211 - Count Collisions on a Road.<p>Medium</p> <p>There are <code>n</code> cars on an infinitely long road. The cars are numbered from <code>0</code> to <code>n - 1</code> from left to right and each car is present at a <strong>unique</strong> point.</p> <p>You are given a <strong>0-indexed</strong> string <code>directions</code> of length <code>n</code>. <code>directions[i]</code> can be either <code>'L'</code>, <code>'R'</code>, or <code>'S'</code> denoting whether the <code>i<sup>th</sup></code> car is moving towards the <strong>left</strong> , towards the <strong>right</strong> , or <strong>staying</strong> at its current point respectively. Each moving car has the <strong>same speed</strong>.</p> <p>The number of collisions can be calculated as follows:</p> <ul> <li>When two cars moving in <strong>opposite</strong> directions collide with each other, the number of collisions increases by <code>2</code>.</li> <li>When a moving car collides with a stationary car, the number of collisions increases by <code>1</code>.</li> </ul> <p>After a collision, the cars involved can no longer move and will stay at the point where they collided. Other than that, cars cannot change their state or direction of motion.</p> <p>Return <em>the <strong>total number of collisions</strong> that will happen on the road</em>.</p> <p><strong>Example 1:</strong></p> <p><strong>Input:</strong> directions = &ldquo;RLRSLL&rdquo;</p> <p><strong>Output:</strong> 5</p> <p><strong>Explanation:</strong> The collisions that will happen on the road are:</p> <ul> <li> <p>Cars 0 and 1 will collide with each other. Since they are moving in opposite directions, the number of collisions becomes 0 + 2 = 2.</p> </li> <li> <p>Cars 2 and 3 will collide with each other. Since car 3 is stationary, the number of collisions becomes 2 + 1 = 3.</p> </li> <li> <p>Cars 3 and 4 will collide with each other. Since car 3 is stationary, the number of collisions becomes 3 + 1 = 4.</p> </li> <li> <p>Cars 4 and 5 will collide with each other. After car 4 collides with car 3, it will stay at the point of collision and get hit by car 5. The number of collisions becomes 4 + 1 = 5.</p> </li> </ul> <p>Thus, the total number of collisions that will happen on the road is 5.</p> <p><strong>Example 2:</strong></p> <p><strong>Input:</strong> directions = &ldquo;LLRR&rdquo;</p> <p><strong>Output:</strong> 0</p> <p><strong>Explanation:</strong> No cars will collide with each other. Thus, the total number of collisions that will happen on the road is 0.</p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= directions.length <= 10<sup>5</sup></code></li> <li><code>directions[i]</code> is either <code>'L'</code>, <code>'R'</code>, or <code>'S'</code>.</li> </ul>

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • countCollisions

      public int countCollisions(String directions)