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].

bool operator < (const Interval &a, const Interval &b){ return a.start < b.start;}
class Solution {
public:
    std::vector<Interval> merge(std::vector<Interval> &intervals) {
        if(intervals.size() == 0) return intervals;
		std::vector<Interval> res;
		std::sort(intervals.begin(),intervals.end());
		int left = intervals[0].start,right = intervals[0].end;
		for (int i = 1; i < intervals.size(); i++)
		{
			if(intervals[i].start <= right)
			{
				right = std::max(right,intervals[i].end);
			}
			else
			{
				res.push_back(Interval(left,right));
				left = intervals[i].start;
				right = intervals[i].end;
			}
		}
		res.push_back(Interval(left,right));
		return res;
    }
};

leetcode - Merge Intervals