From d7527a382e328388ceaf844a0b69f69461e216bc Mon Sep 17 00:00:00 2001
From: Sam Gardner <sam.gardner@digital.homeoffice.gov.uk>
Date: Thu, 22 Feb 2024 15:11:26 +0000
Subject: [PATCH] BAEL-7513 Merge overlapping intervals in collection

---
 .../algorithms/mergeintervals/Interval.java   | 37 +++++++++++++++++++
 .../MergeOverlappingIntervals.java            | 29 +++++++++++++++
 .../MergeIntervalsUnitTest.java               | 30 +++++++++++++++
 3 files changed, 96 insertions(+)
 create mode 100644 algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/mergeintervals/Interval.java
 create mode 100644 algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/mergeintervals/MergeOverlappingIntervals.java
 create mode 100644 algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/mergeintervals/MergeIntervalsUnitTest.java

diff --git a/algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/mergeintervals/Interval.java b/algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/mergeintervals/Interval.java
new file mode 100644
index 0000000000..1b13b8b279
--- /dev/null
+++ b/algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/mergeintervals/Interval.java
@@ -0,0 +1,37 @@
+package com.baeldung.algorithms.mergeintervals;
+
+import java.util.Objects;
+
+public class Interval {
+    int start;
+    int end;
+
+    Interval(int start, int end) {
+        this.start = start;
+        this.end = end;
+    }
+
+    public void setEnd(int end) {
+        this.end = end;
+    }
+
+    @Override
+    public String toString() {
+        return "Interval{" + "start=" + start + ", end=" + end + '}';
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null || getClass() != o.getClass())
+            return false;
+        Interval interval = (Interval) o;
+        return start == interval.start && end == interval.end;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(start, end);
+    }
+}
\ No newline at end of file
diff --git a/algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/mergeintervals/MergeOverlappingIntervals.java b/algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/mergeintervals/MergeOverlappingIntervals.java
new file mode 100644
index 0000000000..ba424772d5
--- /dev/null
+++ b/algorithms-modules/algorithms-miscellaneous-7/src/main/java/com/baeldung/algorithms/mergeintervals/MergeOverlappingIntervals.java
@@ -0,0 +1,29 @@
+package com.baeldung.algorithms.mergeintervals;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class MergeOverlappingIntervals {
+
+    public List<Interval> doMerge(List<Interval> intervals) {
+        // Sort the intervals based on start time
+        intervals.sort((one, two) -> one.start - two.start);
+
+        // Create somewhere to put the merged list, start it off with the earliest starting interval
+        ArrayList<Interval> merged = new ArrayList<>();
+        merged.add(intervals.get(0));
+
+        // Loop over each interval and merge if start time is before the end time of the
+        // previous interval
+        intervals.forEach(interval -> {
+            if (merged.get(merged.size() - 1).end > interval.start) {
+                merged.get(merged.size() - 1).setEnd(interval.end);
+            } else {
+                merged.add(interval);
+            }
+        });
+
+        return merged;
+    }
+
+}
diff --git a/algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/mergeintervals/MergeIntervalsUnitTest.java b/algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/mergeintervals/MergeIntervalsUnitTest.java
new file mode 100644
index 0000000000..5f15fe00f6
--- /dev/null
+++ b/algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/mergeintervals/MergeIntervalsUnitTest.java
@@ -0,0 +1,30 @@
+package com.baeldung.algorithms.mergeintervals;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+
+import org.junit.jupiter.api.Test;
+
+class MergeIntervalsUnitTest {
+
+    private ArrayList<Interval> intervals = new ArrayList<>(Arrays.asList(
+      new Interval(2, 5),
+      new Interval(13, 20),
+      new Interval(11, 15),
+      new Interval(1, 3)
+    ));
+    private ArrayList<Interval> intervalsMerged = new ArrayList<>(Arrays.asList(
+      new Interval(1, 5),
+      new Interval(11, 20)
+    ));
+
+    @Test
+    void givenIntervals_whenMerging_thenReturnMergedIntervals() {
+        MergeOverlappingIntervals merger = new MergeOverlappingIntervals();
+        ArrayList<Interval> result = (ArrayList<Interval>) merger.doMerge(intervals);
+        assertArrayEquals(intervalsMerged.toArray(), result.toArray());
+    }
+
+}