solution.h

#include <vector>
using std::vector;
#include <algorithm>

struct Interval {
    int start;
    int end;
    Interval() : start(0), end(0) {}
    Interval(int s, int e) : start(s), end(e) {}
};

class Solution {
public:
    vector<Interval> merge(vector<Interval> &intervals) {
        vector<Interval> ret;
        std::sort(intervals.begin(), intervals.end(), [](const Interval &a, const Interval &b){
            return a.start < b.start;
        });
        for (const auto &interval : intervals) {
            if (!ret.empty() && interval.start <= ret.back().end)
                ret.back().end = std::max(interval.end, ret.back().end);
            else ret.push_back(interval);
        }
        return ret;
    }
};