[leetcode]Merge Intervals

Merge Intervals

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].

 

算法思路：

将intervals按照start进行排序，然后建立一个空的list，把intervals的元素逐个插入并做合并操作。

值得注意的是：如果intervals的待插入元素能与list的元素合并，则一定是与最后一个合并。think about it

【吐槽】：这是第一遍时候想到的算法，还是很不错的，单次遍历，只不过当时不会用Collections.sort()自己手动的排序了。o(╯□╰)o

/**
 * 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 {
    List<Interval> res = new ArrayList<Interval>();
    public List<Interval> merge(List<Interval> intervals) {
        if(intervals == null || intervals.size() == 0) return res;
        Collections.sort(intervals, new Comparator<Interval>(){
            public int compare(Interval a,Interval b){
                return a.start - b.start;
            }
        });
        List<Interval> list = new ArrayList<Interval>();
        list.add(intervals.get(0));
        for(int i = 1; i < intervals.size(); i++){
            Interval last = list.get(list.size() - 1);
            Interval thus = intervals.get(i);
            if(thus.start <= last.end){
                last.end = thus.end > last.end ? thus.end : last.end;
            }else{
                list.add(thus);
            }
        }
        return list;
    }
}