MergeOverlappingIntervals.java

package com.company;

import java.util.*;

class Interval {
    public int start;
    public int end;

    public Interval(int _start, int _end) {
        start = _start;
        end = _end;
    }
}

public class MergeOverlappingIntervals {
    public static void main(String args[]) {
        MergeOverlappingIntervals mergeOverlappingIntervals = new MergeOverlappingIntervals();
        List<Interval> intervals = new ArrayList<>();
        intervals.add(new Interval(6,8));
        intervals.add(new Interval(1,9));
        intervals.add(new Interval(2,4));
        intervals.add(new Interval(4,7));
        List<Interval> merge = mergeOverlappingIntervals.merge(intervals);
        for(Interval item: merge){
            System.out.println(item.start + " " +  item.end);
        }
    }

    public List<Interval> merge(List<Interval> intervals) {
        Collections.sort(intervals, new Comparator<Interval>() {
            @Override
            public int compare(Interval obj0, Interval obj1) {
                return obj0.start - obj1.start;
            }
        });

        List<Interval> ret = new ArrayList<>();
        Interval prev = null;
        for (Interval inter : intervals) {
            if (prev == null || inter.start > prev.end) {
                ret.add(inter);
                prev = inter;
            } else if (inter.end > prev.end) {
                // Modify the element already in list
                prev.end = inter.end;
            }
        }
        return ret;
    }
}