[LeetCode] 56. 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 {
    
    class IntervalComparator implements Comparator{
        public int compare(Interval a, Interval b){
            return a.start - b.start;
        }
    }
    
    public List merge(List intervals) {
    
        List ret = new ArrayList();
    
        int len = intervals.size();
        
        if(0 == len)
            return ret;
    
        Collections.sort(intervals, new IntervalComparator());
        
        Interval m = intervals.get(0);
        
        for(int i = 1; i < len; ++i){
            Interval c = intervals.get(i);
            if(m.end >= c.start)
            {
                m.end = Math.max(m.end, c.end);
            }else{
                ret.add(m);
                m = c;
            }
        }
        
        ret.add(m);
        
        return ret;
        
    }
}