Merge Intervals

• Time : $O(n)$
• Space : $O(n)$

/**
 * Definition for an interval.
 * struct Interval {
 *     int start;
 *     int end;
 *     Interval() : start(0), end(0) {}
 *     Interval(int s, int e) : start(s), end(e) {}
 * };
 */
vector<Interval> Solution::insert(vector<Interval> &intervals, Interval newInterval) {
    vector<Interval> res;
    bool fl = false;
    int ma = INT_MIN;
    for(auto& i : intervals) {
        if(!fl) {
            if(newInterval.start <= i.start) {
                if(!res.empty() and res.back().end >= newInterval.start) {
                    res.back().end = max(res.back().end, newInterval.end);
                } else res.push_back(newInterval);
                fl = true;
            }
            if(!res.empty() and res.back().end >= i.start) {
                res.back().end = max(res.back().end, i.end);    
            } else res.push_back(i);
        } else {
            if(res.back().end >= i.start) {
                res.back().end = max(res.back().end, i.end);
            } else res.push_back(i);
        }
        if(!fl and res.back().end >= newInterval.start) {
            res.back().end = max(res.back().end, newInterval.end);
            fl = true;
        }
    }
    if(!fl) res.push_back(newInterval);
    return res;
}