56.合并区间

/**
 * 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; }
 * }
 */
class Solution {
    public List<Interval> merge(List<Interval> intervals) {
        List<Integer> list = new ArrayList<>();
        List<Interval> result = new ArrayList<>();
        if(intervals.size() == 0){
            return result;
        }
        HashMap<Integer, Interval> map = new HashMap<>();
        for(int i = 0; i < intervals.size(); i++){
            Interval interval = intervals.get(i);
            if(!map.containsKey(interval.start)){
                list.add(interval.start);
                map.put(interval.start, interval);
            } else {
                Interval lastInterval = map.get(interval.start);
                int end = Math.max(lastInterval.end, interval.end);
                interval = new Interval(lastInterval.start, end);
                map.put(interval.start, interval);
            }
        }
        Collections.sort(list);
        for(int i = 0 ; i < list.size()-1;i++){
            Interval interval = map.get(list.get(i));
            if(interval.end >= list.get(i+1)){
                Interval next = map.get(list.get(i+1));
                Interval mergedInterval = new Interval(interval.start, Math.max(interval.end, next.end));
                map.put(list.get(i+1), mergedInterval);
            } else {
                result.add(interval);
            }
        }
        result.add(map.get(list.get(list.size()-1)));
        return result;
    }
}