OJ---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 {
    public ArrayList<Interval> merge(ArrayList<Interval> intervals) {
        //先将数组列表中的所有区间start进行升序排列
        Collections.sort(intervals,(a1,a2)->a1.start-a2.start);
        ArrayList<Interval> result = new ArrayList<>();
        int n = -1;
        for(Interval i:intervals){
            //如果[a,b][c,d]两个范围中c>b则不需要合并
            if(n==-1||i.start>result.get(n).end){
                result.add(i);
                n++;
            }else{
                //如果需要合并则比较b与d的大小
                result.get(n).end = Math.max(result.get(n).end,i.end);
            }
        }
        return result;
    }
}