56.Merge Intervals

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