56. Merge Intervals

/**
 * 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) {
        if(intervals.size() <= 1)
            return intervals;
        
        // 将 intervals 根据 start 排序
        Collections.sort(intervals, new Comparator<Interval>() {
            @Override
            public int compare(Interval o1, Interval o2) {
                return o1.start - o2.start;
            }
        });
        
        List<Interval> resultList = new LinkedList<>();
        int start = intervals.get(0).start;
        int end = intervals.get(0).end;
        
        for(Interval interval: intervals) {
            if(interval.start <= end) // 有重叠
                end = Math.max(end, interval.end);
            else {                    // 无重叠
                resultList.add(new Interval(start, end));
                start = interval.start;
                end = interval.end;
            }
        }
        resultList.add(new Interval(start, end));
        return resultList;
    }
}