# LeetCode challenge – Merge Intervals – Java Solution

This is a solution for the LeetCode challenge – Merge Intervals written in Java ( Source )

Given a collection of intervals, merge all overlapping intervals.

For example, Given [1,3],[2,6],[8,10],[15,18], return [1,6],[8,10],[15,18].

Solution: O(N log N) where N is the number of intervals 1. Sort the intervals based on start index 2. Mark the first interval as the current interval 3. For every ith interval starting 1 -> N, if the ith interval overlaps with the current interval then create a new current interval. Else, add the current interval to result set and begin a new current interval.

**Example** **1**: Input: flowerbed = [1,0,0,0,1], n = 1 Output: True Example 2: Input: flowerbed = [1,0,0,0,1], n = 2 Output: False Note: The input array won’t violate no-adjacent-flowers rule. The input array size is in the range of [1, 20000]. n is a non-negative integer which won’t exceed the input array size.

import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.List; public class MergeIntervals { public static class Interval { int start; int end; Interval() { start = 0; end = 0; } Interval(int s, int e) { start = s; end = e; } } public static void main(String[] args) throws Exception { Interval i1 = new Interval(1, 2); Interval i2 = new Interval(3, 4); Interval i3 = new Interval(5, 6); Interval i4 = new Interval(1, 10); List<Interval> result = new MergeIntervals().merge(Arrays.asList(i1, i2, i3, i4)); result.forEach((I) -> System.out.println(I.start + " " + I.end)); } public List<Interval> merge(List<Interval> intervals) { if (intervals.isEmpty()) return new ArrayList<>(); Collections.sort(intervals, (o1, o2) -> Integer.compare(o1.start, o2.start)); List<Interval> result = new ArrayList<>(); Interval curr = intervals.get(0); for (int i = 1, l = intervals.size(); i < l; i++) { Interval I = intervals.get(i); if (I.start >= curr.start && I.start <= curr.end) { // check if the new interval overlaps with the current curr.end = curr.end > I.end ? curr.end : I.end; } else { result.add(curr); curr = I; } } result.add(curr); return result; } }