题解 | #合并区间#

import java.util.*;

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

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param intervals Interval类ArrayList
     * @return Interval类ArrayList
     */
    public ArrayList<Interval> merge (ArrayList<Interval> intervals) {
        if (intervals.size() <= 1) {
            return intervals;
        }
        ArrayList<Interval> res = new ArrayList<>();
        int n = intervals.size();
        // 进行排序
        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;
                }
            }
        });
        Interval a = intervals.get(0);
        int left = a.start, right = a.end;
        for (int i = 1; i < n; i++) {
            Interval arr = intervals.get(i);
            // 有重叠部分
            if (right >= arr.start) {
                if (right < arr.end) {
                    right = arr.end;
                }
            } else {
                res.add(new Interval(left, right));
                left = arr.start;
                right = arr.end;
            }
        }
	  // 最后这一步一定要加上
        res.add(new Interval(left, right));
        return res;
    }
}