Solution for "Merge Intervals"

Author: Thuy Trinh

src/main/java/leetcode/meetingrooms/Interval.java

@@ -1,7 +1,7 @@
 package leetcode.meetingrooms;
 
 public class Interval {
-  public final int start;
+  public int start;
   public int end;
 
   public Interval() {
@@ -13,4 +13,18 @@ public Interval(int s, int e) {
     start = s;
     end = e;
   }
+
+  @Override
+  public String toString() {
+    return "[" + start + ", " + end + "]";
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (!(obj instanceof Interval)) {
+      return false;
+    }
+    Interval o = (Interval) obj;
+    return start == o.start && end == o.end;
+  }
 }

src/main/java/leetcode/mergeintervals/Solution.kt

@@ -0,0 +1,30 @@
+package leetcode.mergeintervals
+
+import leetcode.meetingrooms.Interval
+
+/**
+ * https://leetcode.com/problems/merge-intervals/description/
+ */
+class Solution {
+  fun merge(intervals: List<Interval>): List<Interval> = when {
+    intervals.isEmpty() -> emptyList()
+    else -> {
+      val sortedIntervals = intervals.sortedBy { it.start }
+      val mergedIntervals = mutableListOf<Interval>()
+      mergedIntervals += sortedIntervals.first()
+
+      (1..sortedIntervals.lastIndex).forEach {
+        val current = mergedIntervals.last()
+        val next = sortedIntervals[it]
+        when {
+          current.end >= next.start -> {
+            // e.g. [1,4] and [2,3] -> [1,4]
+            current.end = maxOf(current.end, next.end)
+          }
+          else -> mergedIntervals += next
+        }
+      }
+      mergedIntervals
+    }
+  }
+}

src/test/java/leetcode/mergeintervals/SolutionTest.kt

@@ -0,0 +1,32 @@
+package leetcode.mergeintervals
+
+import leetcode.meetingrooms.Interval
+import org.amshove.kluent.shouldEqual
+import org.junit.Test
+
+class SolutionTest {
+  @Test
+  fun test() {
+    Solution().merge(listOf(
+        Interval(1, 3),
+        Interval(2, 6),
+        Interval(8, 10),
+        Interval(15, 18)
+    )).shouldEqual(listOf(
+        Interval(1, 6),
+        Interval(8, 10),
+        Interval(15, 18)
+    ))
+    Solution().merge(listOf(
+        Interval(1, 4),
+        Interval(2, 3)
+    )).shouldEqual(listOf(
+        Interval(1, 4)
+    ))
+    Solution().merge(listOf(
+        Interval(1, 3)
+    )).shouldEqual(listOf(
+        Interval(1, 3)
+    ))
+  }
+}