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Add Merge Intervals algorithm (TheAlgorithms#5516)
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‎DIRECTORY.md‎

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* [SearchSinglyLinkedListRecursion](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/SearchSinglyLinkedListRecursion.java)
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* [SinglyLinkedList](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/SinglyLinkedList.java)
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* [SkipList](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/SkipList.java)
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* [SortedLinkedList](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/SortedLinkedList.java)
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* [Node](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/Node.java)
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* queues
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* [CircularQueue](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/queues/CircularQueue.java)
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* [FractionalKnapsack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/FractionalKnapsack.java)
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* [GaleShapley](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/GaleShapley.java)
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* [JobSequencing](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/JobSequencing.java)
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* [MergeIntervals](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/MergeIntervals.java)
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* [MinimizingLateness](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/MinimizingLateness.java)
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* io
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* [BufferedReader](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/io/BufferedReader.java)
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* [TowerOfHanoi](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/others/TowerOfHanoi.java)
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* [TwoPointers](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/others/TwoPointers.java)
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* [Verhoeff](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/others/Verhoeff.java)
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* Recursion
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* [GenerateSubsets](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/Recursion/GenerateSubsets.java)
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* scheduling
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* [FCFSScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/FCFSScheduling.java)
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* [PreemptivePriorityScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/PreemptivePriorityScheduling.java)
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* [CombSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/CombSort.java)
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* [CountingSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/CountingSort.java)
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* [CycleSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/CycleSort.java)
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* [DNFSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/DNFSort.java)
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* [DualPivotQuickSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/DualPivotQuickSort.java)
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* [DutchNationalFlagSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/DutchNationalFlagSort.java)
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* [ExchangeSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/ExchangeSort.java)
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* [RotateSinglyLinkedListsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedListsTest.java)
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* [SinglyLinkedListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/lists/SinglyLinkedListTest.java)
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* [SkipListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/lists/SkipListTest.java)
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* [SortedLinkedListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/lists/SortedLinkedListTest.java)
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* queues
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* [CircularQueueTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/CircularQueueTest.java)
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* [DequeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/DequeTest.java)
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* [FractionalKnapsackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/FractionalKnapsackTest.java)
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* [GaleShapleyTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/GaleShapleyTest.java)
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* [JobSequencingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/JobSequencingTest.java)
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* [MergeIntervalsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/MergeIntervalsTest.java)
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* [MinimizingLatenessTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/MinimizingLatenessTest.java)
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* io
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* [BufferedReaderTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/io/BufferedReaderTest.java)
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* [TestPrintMatrixInSpiralOrder](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/TestPrintMatrixInSpiralOrder.java)
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* [TwoPointersTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/TwoPointersTest.java)
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* [WorstFitCPUTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/WorstFitCPUTest.java)
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* Recursion
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* [GenerateSubsetsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/Recursion/GenerateSubsetsTest.java)
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* scheduling
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* [FCFSSchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/FCFSSchedulingTest.java)
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* [PreemptivePrioritySchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/PreemptivePrioritySchedulingTest.java)

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

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package com.thealgorithms.greedyalgorithms;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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/**
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* Problem Statement:
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* Given an array of intervals where intervals[i] = [starti, endi].
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*
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* Merge all overlapping intervals and return an array of the non-overlapping
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* intervals
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* that cover all the intervals in the input.
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*/
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public final class MergeIntervals {
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/**
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* Private constructor to prevent instantiation of this utility class.
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*/
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private MergeIntervals() {
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}
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/**
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* Merges overlapping intervals from the given array of intervals.
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*
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* The method sorts the intervals by their start time, then iterates through the
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* sorted intervals
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* and merges overlapping intervals. If an interval overlaps with the last
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* merged interval,
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* it updates the end time of the last merged interval. Otherwise, it adds the
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* interval as a new entry.
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*
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* @param intervals A 2D array representing intervals where each element is an
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* interval [starti, endi].
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* @return A 2D array of merged intervals where no intervals overlap.
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*
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* Example:
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* Input: {{1, 3}, {2, 6}, {8, 10}, {15, 18}}
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* Output: {{1, 6}, {8, 10}, {15, 18}}
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*/
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public static int[][] merge(int[][] intervals) {
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// Sort the intervals by their start time (ascending order)
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Arrays.sort(intervals, (a, b) -> Integer.compare(a[0], b[0]));
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// List to store merged intervals
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List<int[]> merged = new ArrayList<>();
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for (int[] interval : intervals) { // Each interval
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// If the merged list is empty or the current interval does not overlap with
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// the last merged interval, add it to the merged list.
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if (merged.isEmpty() || interval[0] > merged.get(merged.size() - 1)[1]) {
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merged.add(interval);
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} else {
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// If there is an overlap, merge the intervals by updating the end time
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// of the last merged interval to the maximum end time between the two
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// intervals.
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merged.get(merged.size() - 1)[1] = Math.max(merged.get(merged.size() - 1)[1], interval[1]);
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}
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}
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// Convert the list of merged intervals back to a 2D array and return it
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return merged.toArray(new int[merged.size()][]);
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}
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}

‎src/test/java/com/thealgorithms/greedyalgorithms/MergeIntervalsTest.java‎

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package com.thealgorithms.greedyalgorithms;
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import static org.junit.jupiter.api.Assertions.assertArrayEquals;
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import org.junit.jupiter.api.Test;
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public class MergeIntervalsTest {
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@Test
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public void testMergeIntervalsWithOverlappingIntervals() {
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// Test case where some intervals overlap and should be merged
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int[][] intervals = {{1, 3}, {2, 6}, {8, 10}, {15, 18}};
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int[][] expected = {{1, 6}, {8, 10}, {15, 18}};
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int[][] result = MergeIntervals.merge(intervals);
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assertArrayEquals(expected, result);
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}
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@Test
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public void testMergeIntervalsWithNoOverlap() {
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// Test case where intervals do not overlap
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int[][] intervals = {{1, 2}, {3, 4}, {5, 6}};
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int[][] expected = {{1, 2}, {3, 4}, {5, 6}};
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int[][] result = MergeIntervals.merge(intervals);
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assertArrayEquals(expected, result);
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}
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@Test
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public void testMergeIntervalsWithCompleteOverlap() {
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// Test case where intervals completely overlap
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int[][] intervals = {{1, 5}, {2, 4}, {3, 6}};
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int[][] expected = {{1, 6}};
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int[][] result = MergeIntervals.merge(intervals);
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assertArrayEquals(expected, result);
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}
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@Test
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public void testMergeIntervalsWithSingleInterval() {
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// Test case where only one interval is given
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int[][] intervals = {{1, 2}};
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int[][] expected = {{1, 2}};
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int[][] result = MergeIntervals.merge(intervals);
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assertArrayEquals(expected, result);
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}
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@Test
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public void testMergeIntervalsWithEmptyArray() {
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// Test case where the input array is empty
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int[][] intervals = {};
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int[][] expected = {};
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int[][] result = MergeIntervals.merge(intervals);
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assertArrayEquals(expected, result);
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}
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@Test
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public void testMergeIntervalsWithIdenticalIntervals() {
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// Test case where multiple identical intervals are given
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int[][] intervals = {{1, 3}, {1, 3}, {1, 3}};
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int[][] expected = {{1, 3}};
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int[][] result = MergeIntervals.merge(intervals);
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assertArrayEquals(expected, result);
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}
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@Test
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public void testMergeIntervalsWithRandomIntervals() {
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// Test case with a mix of overlapping and non-overlapping intervals
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int[][] intervals = {{1, 4}, {5, 7}, {2, 6}, {8, 10}};
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int[][] expected = {{1, 7}, {8, 10}};
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int[][] result = MergeIntervals.merge(intervals);
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assertArrayEquals(expected, result);
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}
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}

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