leetcode:Merge Interval

1、

　　Given a collection of intervals, merge all overlapping intervals.

[                     [
  [1, 3],               [1, 6],
  [2, 6],      =>       [8, 10],
  [8, 10],              [15, 18]
  [15, 18]            ]
]
2、思路
　　1、对所有的集合排个序，按小到大
　　2、迭代判断，从第一个判断，如果第二个的start 小于第一个的end，end重新判断
　　3、如果大于，间断，添加到集合里面
　　4、最后，添加进集合。
3、代码
　　

public class MergeIntervals {

    public ArrayList<Interval> merge(ArrayList<Interval> intervals) {
        if (intervals == null || intervals.size() <= 1) {
            return intervals;
        }
               //排序
        Collections.sort(intervals, new IntervalComparator());
        ArrayList<Interval> result = new ArrayList<Interval>();
        Interval last = intervals.get(0);
        for (int i = 1; i < intervals.size(); i++) {
            Interval curt = intervals.get(i);
//区间判断
            if (curt.start <= last.end) {
                last.end = Math.max(last.end, curt.end);
            } else {
                result.add(last);
                last = curt;
            }
        }
        result.add(last);
        return result;
    }

    private class IntervalComparator implements Comparator<Interval> {
        public int compare(Interval a, Interval b) {
            return a.start - b.start;
        }
    }
}

 class Interval {
        int start, end;
        Interval(int start, int end) {
             this.start = start;
             this.end = end;
         }
 }