[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].

思路：

首先，将 intervals排序，然后随时比较前一个的end与后一个的start的关系，及时更新返回值。

vector<Interval> merge(vector<Interval>& intervals)
     {
         int n = intervals.size();
         vector<Interval> ret;
         if (n <= 1)return intervals;
         sort(intervals.begin(), intervals.end(), [](Interval a, Interval b){return a.start < b.start;});
         ret.push_back(intervals[0]);
         for (int i = 1; i < n; i++)
         {
             if (ret.back().end < intervals[i].start)ret.push_back(intervals[i]);
             else ret.back().end = max(ret.back().end , intervals[i].end);             
         }
         return ret;
     }

参考：

https://discuss.leetcode.com/topic/20263/c-10-line-solution-easing-understanding