mergeIntervals.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].

/**
 * 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 List<Interval> merge(List<Interval> intervals) {
        
        if(intervals.size() <= 1) {
            
            return intervals;
            
        }
        
         // Sort by ascending starting point using an anonymous Comparator
        Collections.sort(intervals, new Comparator<Interval>() {
            @Override
            public int compare(Interval i1, Interval i2) {
                return Integer.compare(i1.start, i2.start);
            }
        });
        
        List<Interval> result = new ArrayList<Interval>();

        int start = intervals.get(0).start;
        int end = intervals.get(0).end;
        
        for(Interval interval : intervals) {
            
            if(interval.start <= end) {
                
                end = Math.max(end, interval.end);
                
            }
            
            else {
                
                result.add(new Interval(start, end));
                start = interval.start;
                end = interval.end;
                
            }
            
        }
        
        result.add(new Interval(start, end));
        
        return result;

    }

}