【LeetCode】56.Merge Intervals(Medium)解题报告

【LeetCode】56.Merge Intervals(Medium)解题报告

题目地址：https://leetcode.com/problems/merge-intervals/description/

题目描述：

  Given a collection of intervals, merge all overlapping intervals.

  For example, Given [1,3],[2,6],[8,10],[15,18], return [1,6],[8,10],[15,18].

  非常重要，面试经常出现。扫描线算法这道题很经典的解法，前面meeting room的方法也可以用到这道题上。

Solution:

/**
* 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; }
* }
*/
//time:O(nlogn)
//space:O(n)
class Solution {
public List<Interval> merge(List<Interval> intervals) {
if(intervals == null || intervals.size() <=1) return intervals;
//数据不是Array，list可以用Collections.sort()排序
Collections.sort(intervals,(a,b)->a.start - b.start);
int start = intervals.get(0).start;
int end = intervals.get(0).end;
List<Interval> res = new ArrayList<>();
for(Interval interval : intervals){
if(interval.start <= end){
end = Math.max(end , interval.end);
}else{
res.add(new Interval(start,end));
start = interval.start;
end = interval.end;
}
}
//把最后一个加进去
res.add(new Interval(start,end));
return res;
}
}

Date：2018年2月19日