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HardvanHardvan
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Improve comments in ActivitySelection.java (TheAlgorithms#5485)
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Lines changed: 46 additions & 15 deletions

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‎DIRECTORY.md‎

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* [LongestNonRepetitiveSubstring](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/LongestNonRepetitiveSubstring.java)
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* [LongestPalindromicSubstring](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/LongestPalindromicSubstring.java)
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* [Lower](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Lower.java)
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* [Manacher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Manacher.java)
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* [MyAtoi](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/MyAtoi.java)
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* [Palindrome](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Palindrome.java)
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* [Pangram](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Pangram.java)
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* [TwinPrimeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/TwinPrimeTest.java)
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* [VolumeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/VolumeTest.java)
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* misc
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* [ColorContrastRatioTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/ColorContrastRatioTest.java)
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* [InverseOfMatrixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/InverseOfMatrixTest.java)
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* [MapReduceTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MapReduceTest.java)
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* [MedianOfMatrixtest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MedianOfMatrixtest.java)
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* [MedianOfRunningArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MedianOfRunningArrayTest.java)
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* [ArrayRightRotation](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/ArrayRightRotation.java)
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* [ArrayRightRotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/ArrayRightRotationTest.java)
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* [BestFitCPUTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/BestFitCPUTest.java)
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* [BFPRTTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/BFPRTTest.java)
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* [BoyerMooreTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/BoyerMooreTest.java)
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* cn
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* [HammingDistanceTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/cn/HammingDistanceTest.java)
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* [LongestNonRepetitiveSubstringTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/LongestNonRepetitiveSubstringTest.java)
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* [LongestPalindromicSubstringTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/LongestPalindromicSubstringTest.java)
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* [LowerTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/LowerTest.java)
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* [ManacherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/ManacherTest.java)
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* [MyAtoiTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/MyAtoiTest.java)
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* [PalindromeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/PalindromeTest.java)
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* [PangramTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/strings/PangramTest.java)

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

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

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