Merge collection of intervals in Java

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].

The key to solving this problem is defining a Comparator first to sort the ArrayList of Intervals. And then merge some intervals. The take-away message from this problem is utilizing the advantage of sorted list/array

class Interval {
int start;
int end;
Interval() {
start = 0;
end = 0;
}
Interval(int s, int e) {
start = s;
end = e;
}
}
public class Solution {
public ArrayList<Interval> merge(ArrayList<Interval> intervals) {
if (intervals == null || intervals.size() <= 1)
return intervals;
// sort intervals by using self-defined Comparator
Collections.sort(intervals, new IntervalComparator());
ArrayList<Interval> result = new ArrayList<Interval>();
Interval prev = intervals.get(0);
for (int i = 1; i < intervals.size(); i++) {
Interval curr = intervals.get(i);
if (prev.end >= curr.start) {
// merged case
Interval merged = new Interval(prev.start, Math.max(prev.end,
curr.end));
prev = merged;
} else {
result.add(prev);
prev = curr;
}
}
result.add(prev);
return result;
}
}
class IntervalComparator implements Comparator<Interval> {
public int compare(Interval i1, Interval i2) {
return i1.start - i2.start;
}
}

Insert Interval in Java

Given a set of non-overlapping & sorted intervals, insert a new interval into the intervals
Example 1:
Given intervals [1,3],[6,9], insert and merge [2,5] in as [1,5],[6,9].
Example 2:
Given [1,2],[3,5],[6,7],[8,10],[12,16], insert and merge [4,9] in as [1,2],[3,10],[12,16].
This is because the new interval [4,9] overlaps with [3,5],[6,7],[8,10].

/**
* Definition for an interval.
* public class Interval {
* int start;
* int end;
* Interval() { start = 0; end = 0; }
* Interval(int s, int e) { start = s; end = e; }
* }
*/
public class Solution {
public ArrayList<Interval> insert(ArrayList<Interval> intervals, Interval
newInterval) {
ArrayList<Interval> result = new ArrayList<Interval>();
for(Interval interval: intervals){
if(interval.end < newInterval.start){
result.add(interval);
}else if(interval.start > newInterval.end){
result.add(newInterval);
newInterval = interval;
}else if(interval.end >= newInterval.start || interval.start <=
newInterval.end){
newInterval = new Interval(Math.min(interval.start,
newInterval.start), Math.max(newInterval.end, interval.end));
}
}
result.add(newInterval);
return result;
}
}