Merge Intervals

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].

Solution: 1. Sort in ascending order of 'start'.
2. Traverse the 'intervals', merge or push...

/**
 * Definition for an interval.
 * struct Interval {
 *     int start;
 *     int end;
 *     Interval() : start(0), end(0) {}
 *     Interval(int s, int e) : start(s), end(e) {}
 * };
 */

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