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 {
    public ArrayList<Interval> merge(ArrayList<Interval> intervals) {
        // 返回值
        ArrayList<Interval> res = new ArrayList();

        // 需要对原集合进行排序
        intervals.sort((Interval i1,Interval i2) -> {return i1.start - i2.start;});

        // 从头开始
        int i = 0;

        while(i < intervals.size()){

            // 最后一个值必定返回
            if(i == intervals.size()-1){
                res.add(intervals.get(i));
                return res;
            }

            // 存在多种情况

            if(intervals.get(i).end >= intervals.get(i+1).start && intervals.get(i).end < intervals.get(i+1).end){// 第一种：接壤
                intervals.get(i+1).start = intervals.get(i).start;
                i++;
            }else if(intervals.get(i).end >= intervals.get(i+1).start && intervals.get(i).end >= intervals.get(i+1).end){// 第二种：包含
                intervals.get(i+1).start = intervals.get(i).start;
                intervals.get(i+1).end = intervals.get(i).end;
                i++;
            }else{// 第三种：无关，无关时将其加入即可
                res.add(intervals.get(i));
                i++;
            }      
            
        }

        return res;
    }
}