156. Merge Intervals【LintCode by java】

Description

Given a collection of intervals, merge all overlapping intervals.

Example

Given intervals => merged intervals:

[                     [
  (1, 3),               (1, 6),
  (2, 6),      =>       (8, 10),
  (8, 10),              (15, 18)
  (15, 18)            ]
]

Challenge

O(n log n) time and O(1) extra space.

题意:给定一个集合,里面有若干无序区间,要求将有重叠部分的区间合并。这个题目的示例给的不是很好,这个示例给人的感觉好像这些区间是有序的。有序和无序,用同样的方法做,结果可能不一样,比如我一开始理解成有序,报错如下:

Input
[(2,3),(4,5),(6,7),(8,9),(1,10)]
Output
[(2,3),(4,5),(6,7),(1,10)]
Expected
[(1,10)]
Hint
Review your code and make sure your algorithm is correct. Wrong answer usually caused by typos if your algorithm is correct.
Input test data (one parameter per line.)

虽然它本来无序,但我们也可以人为地将它根据first值的大小进行排序,可以使用Collections类中的sort方法(查一下API)对List进行排序。排完之后,就可以对集合内的区间进行合并了。合并的方法与此题类似:30. Insert Interval【LintCode by java】

申请一个新的集合,再用一个循环,将排好序的区间两两比较,如果无需合并,则将前者加入新的集合,后者继续与后面的区间比较合并。代码如下:

 1 public class Solution {
 2     /**
 3      * @param intervals: interval list.
 4      * @return: A new interval list.
 5      */
 6      //判断两区间是否相交
 7     public List<Interval> merge(List<Interval> intervals) {
 8         // write your code here
 9         if(intervals.size()==0||intervals.size()==1)
10            return intervals;
11         List<Interval>res=new ArrayList<Interval>();
12         Collections.sort(intervals,new IntervalCompare());
13         Interval last=intervals.get(0);
14         for(int i=1;i<intervals.size();i++){
15             Interval cur=intervals.get(i);
16             if(last.end<cur.start){
17                 res.add(last);
18                 last=cur;
19             }else{
20                 last.start=Math.min(last.start,cur.start);
21                 last.end=Math.max(last.end,cur.end);
22             }
23         }
24         res.add(last);
25         return res;
26     }
27       private class IntervalCompare implements Comparator<Interval>{
28         public int compare(Interval a,Interval b){
29             return a.start-b.start;
30         }
31     }
32 }

如有错误,欢迎批评指正~

原文地址:https://www.cnblogs.com/phdeblog/p/9111599.html

时间: 2024-10-29 19:54:05

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