leetcode 56. 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].

这个题的难点在于，怎么去对Interval类型进行排序，在屡次失败之后，在别人的博客学到了，要自己重写Comparator，写好之后就是一个O(n)的线性复杂度的合并问题了

/** * 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 List<Interval> merge(List<Interval> intervals) {        if (intervals.size()<=1)return intervals;        Collections.sort(intervals,new IntervalComparator());        List<Interval> list = new ArrayList<Interval>();        Interval pre = intervals.get(0);        for(int i=1;i<intervals.size();i++){            Interval cur = intervals.get(i);            if(pre.end>=cur.start){                Interval merged = new Interval(pre.start,Math.max(pre.end,cur.end));                pre = merged;            }            else {                list.add(pre);                pre = cur;            }        }        list.add(pre);        return list;    }}class IntervalComparator implements Comparator<Interval>{    public int compare(Interval a,Interval b){        return a.start - b.start;    }}