Add Merge Intervals algorithm (#5516)

2025-07-07 17:56:02 +08:00 · 2024-10-03 12:37:44 +05:30
parent ea0ed23961
commit ce6d98f8da
3 changed files with 143 additions and 1 deletions
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@ -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)
--- a/src/main/java/com/thealgorithms/greedyalgorithms/MergeIntervals.java
+++ b/src/main/java/com/thealgorithms/greedyalgorithms/MergeIntervals.java
@ -0,0 +1,64 @@
+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()][]);
+    }
+}
--- a/src/test/java/com/thealgorithms/greedyalgorithms/MergeIntervalsTest.java
+++ b/src/test/java/com/thealgorithms/greedyalgorithms/MergeIntervalsTest.java
@ -0,0 +1,71 @@
+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);
+    }
+}