Added comments

Author: NilayBadjatya

src/main/java/com/thealgorithms/simulation/NRobotsCollision.java

@@ -1,6 +1,21 @@
 package com.thealgorithms.simulation;
 
+/**
+ * NRobotsCollision simulates the movement of N robots on a 1D line and determines
+ * the earliest time at which any two robots collide.
+ *
+ * <p>Each robot has an initial integer position and a direction of movement
+ * ('R' for right, 'L' for left). All robots move simultaneously at the same speed.
+ * A collision occurs when a right-moving robot and a left-moving robot meet.
+ * The time of collision between two adjacent (in sorted order) robots moving toward
+ * each other is half the distance between them.
+ *
+ * <p>If no two robots ever collide, the method returns -1.
+ */
 public class NRobotsCollision {
+    /**
+     * Pair holds a robot's position and its direction of movement.
+     */
     static class Pair {
         int first;
         char second;
@@ -9,6 +24,19 @@ static class Pair {
             this.second = second;
         }
     }
+    /**
+     * Finds the earliest time at which any two robots collide.
+     *
+     * <p>Robots are sorted by position. A collision can only happen between a robot
+     * moving right ('R') and the next robot (in sorted order) moving left ('L').
+     * The collision time for such a pair is {@code (posL - posR) / 2}.
+     *
+     * @param n          the number of robots
+     * @param positions  an array of initial positions of the robots
+     * @param directions a string where each character is 'L' or 'R', representing
+     *                   the direction of the corresponding robot
+     * @return the earliest collision time, or -1 if no collision occurs
+     */
     public static int earliestCollisionTime(int n, int[] positions, String directions) {
         List<Pair> sortedDirections = new ArrayList<>();
         for(int i = 0; i < n; i++){