Improve comments in ActivitySelection.java (#5485)

DIRECTORY.md

@@ -560,6 +560,7 @@
             * [LongestNonRepetitiveSubstring](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/LongestNonRepetitiveSubstring.java)
             * [LongestPalindromicSubstring](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/LongestPalindromicSubstring.java)
             * [Lower](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Lower.java)
+            * [Manacher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Manacher.java)
             * [MyAtoi](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/MyAtoi.java)
             * [Palindrome](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Palindrome.java)
             * [Pangram](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Pangram.java)
@@ -846,6 +847,8 @@
             * [TwinPrimeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/TwinPrimeTest.java)
             * [VolumeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/VolumeTest.java)
           * misc
+            * [ColorContrastRatioTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/ColorContrastRatioTest.java)
+            * [InverseOfMatrixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/InverseOfMatrixTest.java)
             * [MapReduceTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MapReduceTest.java)
             * [MedianOfMatrixtest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MedianOfMatrixtest.java)
             * [MedianOfRunningArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MedianOfRunningArrayTest.java)
@@ -857,6 +860,7 @@
             * [ArrayRightRotation](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/ArrayRightRotation.java)
             * [ArrayRightRotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/ArrayRightRotationTest.java)
             * [BestFitCPUTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/BestFitCPUTest.java)
+            * [BFPRTTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/BFPRTTest.java)
             * [BoyerMooreTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/BoyerMooreTest.java)
             * cn
               * [HammingDistanceTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/cn/HammingDistanceTest.java)
@@ -976,6 +980,7 @@
             * [LongestNonRepetitiveSubstringTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/LongestNonRepetitiveSubstringTest.java)
             * [LongestPalindromicSubstringTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/LongestPalindromicSubstringTest.java)
             * [LowerTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/LowerTest.java)
+            * [ManacherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/ManacherTest.java)
             * [MyAtoiTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/MyAtoiTest.java)
             * [PalindromeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/PalindromeTest.java)
             * [PangramTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/PangramTest.java)

src/main/java/com/thealgorithms/greedyalgorithms/ActivitySelection.java

@@ -4,39 +4,65 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Comparator;
 
-// Problem Link:  https://en.wikipedia.org/wiki/Activity_selection_problem
+// Problem Link: https://en.wikipedia.org/wiki/Activity_selection_problem
 
 public final class ActivitySelection {
+
+    // Private constructor to prevent instantiation of the utility class
     private ActivitySelection() {
     }
-    // Function to perform activity selection
+
+    /**
+     * Function to perform activity selection using a greedy approach.
+     *
+     * The goal is to select the maximum number of activities that don't overlap
+     * with each other, based on their start and end times. Activities are chosen
+     * such that no two selected activities overlap.
+     *
+     * @param startTimes Array containing the start times of the activities.
+     * @param endTimes   Array containing the end times of the activities.
+     * @return A list of indices representing the selected activities that can be
+     *         performed without overlap.
+     */
     public static ArrayList<Integer> activitySelection(int[] startTimes, int[] endTimes) {
         int n = startTimes.length;
+
+        // Create a 2D array to store activity indices along with their start and end
+        // times.
+        // Each row represents an activity in the format: [activity index, start time,
+        // end time].
         int[][] activities = new int[n][3];
 
-        // Create a 2D array to store activities and their start/end times.
-        // Each row: [activity index, start time, end time]
-
+        // Populate the 2D array with the activity index, start time, and end time.
         for (int i = 0; i < n; i++) {
-            activities[i][0] = i; // Assign activity index
-            activities[i][1] = startTimes[i]; // Assign start time
-            activities[i][2] = endTimes[i]; // Assign end time
+            activities[i][0] = i; // Assign the activity index
+            activities[i][1] = startTimes[i]; // Assign the start time of the activity
+            activities[i][2] = endTimes[i]; // Assign the end time of the activity
         }
 
-        // Sort activities by their end times in ascending order.
+        // Sort activities based on their end times in ascending order.
+        // This ensures that we always try to finish earlier activities first.
         Arrays.sort(activities, Comparator.comparingDouble(activity -> activity[2]));
-        int lastEndTime;
+        int lastEndTime; // Variable to store the end time of the last selected activity
+        // List to store the indices of selected activities
         ArrayList<Integer> selectedActivities = new ArrayList<>();
-        selectedActivities.add(activities[0][0]);
-        lastEndTime = activities[0][2];
 
-        // Iterate through sorted activities to select compatible ones.
+        // Select the first activity (as it has the earliest end time after sorting)
+        selectedActivities.add(activities[0][0]); // Add the first activity index to the result
+        lastEndTime = activities[0][2]; // Keep track of the end time of the last selected activity
+
+        // Iterate over the sorted activities to select the maximum number of compatible
+        // activities.
         for (int i = 1; i < n; i++) {
+            // If the start time of the current activity is greater than or equal to the
+            // end time of the last selected activity, it means there's no overlap.
             if (activities[i][1] >= lastEndTime) {
-                selectedActivities.add(activities[i][0]);
-                lastEndTime = activities[i][2];
+                selectedActivities.add(activities[i][0]); // Select this activity
+                lastEndTime = activities[i][2]; // Update the end time of the last selected activity
             }
         }
+
+        // Return the list of selected activity indices.
         return selectedActivities;
     }
 }