vector<Interval> merge(vector<Interval> &intervals) {

vector<Interval> ret;

if (intervals.empty()) {

return ret;

}

std::sort(intervals.begin(), intervals.end(), lc);

Interval cur = intervals[0];

size_t len = intervals.size();

int i = 1;

while (i < len) {

if (cur.end >= intervals[i].start) {

cur.end = max(intervals[i].end,cur.end);

}

else{

ret.push_back(cur);

cur = intervals[i];

}

i++;

}

if (ret.empty() || ret.back().end < cur.start) {

ret.push_back(cur);

}

return ret;

}