题解 | #合并区间#

import java.util.*;
/**
 * 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 {
    ArrayList<Interval> res = new ArrayList<>();
    public ArrayList<Interval> merge(ArrayList<Interval> intervals) {

        if(intervals == null || intervals.size() == 0) return res;
        if(intervals.size() == 1) return intervals;

        Collections.sort(intervals, new Comparator<Interval>() {
            public int compare(Interval o1, Interval o2) {
               if(o1.start != o2.start)
                    return o1.start - o2.start;
                else
                    return o1.end - o2.end;
            }
        });

        res.add(intervals.get(0)); //加入第一个元素
        //后面所有元素与res中的最后一个元素进行对比

        for(int i = 1 ; i < intervals.size() ; i++){
                if(res.get(res.size() - 1).end >= intervals.get(i).start){
                    res.get(res.size() - 1).end = Math.max(res.get(res.size() - 1).end,intervals.get(i).end);
                }else{
                    res.add(intervals.get(i));
                }
        }

        
      

        return res;
    }
}