Merge Intervals

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 {
    private class IntervalComparator implements Comparator<Interval>
    {
        public int compare(Interval a, Interval b) {
            return a.start - b.start;
        }
    }
    public ArrayList<Interval> merge(ArrayList<Interval> intervals) {
        if (intervals.size()<=1) {
            return intervals;
        }
        Collections.sort(intervals, new IntervalComparator());
        ArrayList<Interval> result = new ArrayList<Interval>();
        Interval pre = intervals.get(0);
        for (int i=1;i<intervals.size();i++) {
            Interval current = intervals.get(i);
            if (pre.end >= current.start) {
                //修正PRE 但是不能立刻添加到结果中
                pre.end = Math.max(current.end, pre.end);
                continue;
            }
            result.add(pre);
            pre = current;
        }
        result.add(pre);
        return result;
    }
}