Add Merge Intervals algorithm (#5516)

This commit is contained in:
Hardik Pawar
2024-10-03 12:37:44 +05:30
committed by GitHub
parent ea0ed23961
commit ce6d98f8da
3 changed files with 143 additions and 1 deletions

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@ -156,6 +156,7 @@
* [SearchSinglyLinkedListRecursion](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/SearchSinglyLinkedListRecursion.java)
* [SinglyLinkedList](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/SinglyLinkedList.java)
* [SkipList](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/SkipList.java)
* [SortedLinkedList](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/lists/SortedLinkedList.java)
* [Node](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/Node.java)
* queues
* [CircularQueue](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/queues/CircularQueue.java)
@ -268,6 +269,7 @@
* [FractionalKnapsack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/FractionalKnapsack.java)
* [GaleShapley](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/GaleShapley.java)
* [JobSequencing](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/JobSequencing.java)
* [MergeIntervals](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/MergeIntervals.java)
* [MinimizingLateness](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/MinimizingLateness.java)
* io
* [BufferedReader](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/io/BufferedReader.java)
@ -451,6 +453,8 @@
* [TowerOfHanoi](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/others/TowerOfHanoi.java)
* [TwoPointers](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/others/TwoPointers.java)
* [Verhoeff](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/others/Verhoeff.java)
* Recursion
* [GenerateSubsets](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/Recursion/GenerateSubsets.java)
* scheduling
* [FCFSScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/FCFSScheduling.java)
* [PreemptivePriorityScheduling](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/scheduling/PreemptivePriorityScheduling.java)
@ -500,7 +504,6 @@
* [CombSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/CombSort.java)
* [CountingSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/CountingSort.java)
* [CycleSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/CycleSort.java)
* [DNFSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/DNFSort.java)
* [DualPivotQuickSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/DualPivotQuickSort.java)
* [DutchNationalFlagSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/DutchNationalFlagSort.java)
* [ExchangeSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/ExchangeSort.java)
@ -685,6 +688,7 @@
* [RotateSinglyLinkedListsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/lists/RotateSinglyLinkedListsTest.java)
* [SinglyLinkedListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/lists/SinglyLinkedListTest.java)
* [SkipListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/lists/SkipListTest.java)
* [SortedLinkedListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/lists/SortedLinkedListTest.java)
* queues
* [CircularQueueTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/CircularQueueTest.java)
* [DequeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/DequeTest.java)
@ -754,6 +758,7 @@
* [FractionalKnapsackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/FractionalKnapsackTest.java)
* [GaleShapleyTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/GaleShapleyTest.java)
* [JobSequencingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/JobSequencingTest.java)
* [MergeIntervalsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/MergeIntervalsTest.java)
* [MinimizingLatenessTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/MinimizingLatenessTest.java)
* io
* [BufferedReaderTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/io/BufferedReaderTest.java)
@ -893,6 +898,8 @@
* [TestPrintMatrixInSpiralOrder](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/TestPrintMatrixInSpiralOrder.java)
* [TwoPointersTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/TwoPointersTest.java)
* [WorstFitCPUTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/WorstFitCPUTest.java)
* Recursion
* [GenerateSubsetsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/Recursion/GenerateSubsetsTest.java)
* scheduling
* [FCFSSchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/FCFSSchedulingTest.java)
* [PreemptivePrioritySchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/PreemptivePrioritySchedulingTest.java)

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

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