Given a collection of intervals, merge all overlapping intervals.

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; }
 * }
 */

import java.util.*;
public class Solution {
    public ArrayList<Interval> merge(ArrayList<Interval> intervals) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(intervals.size() == 0) return intervals;
        ArrayList<Interval> ret = new ArrayList<Interval>();
        Collections.sort(intervals, INTERVAL_ORDER);
        
        Iterator<Interval> itr = intervals.iterator();
        
        int start = intervals.get(0).start;
        int end = intervals.get(0).end;
        while(itr.hasNext()) {
            Interval tmp = itr.next();
            if(end >= tmp.start) {
                end = Math.max(end, tmp.end);
            } else {
                ret.add(new Interval(start, end));
                start = tmp.start;
                end = tmp.end;
            }
        }
        ret.add(new Interval(start, end));
        
        return ret;
    }
    
    static final Comparator<Interval> INTERVAL_ORDER = new Comparator<Interval>() {
        public int compare(Interval i, Interval j) {
            return new Integer(i.start).compareTo(new Integer(j.start));
        }
    };

}