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].

    bool compare(const Interval & ls, const Interval & rs){
        return ls.start < rs.start;
    } 
class Solution {
public:
    vector<Interval> merge(vector<Interval> &intervals) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<Interval> ans;
        if (!intervals.size()) return ans;
        sort(intervals.begin(),intervals.end(),compare);
        
        Interval temp = intervals[0];
        for(int i = 1; i < intervals.size(); i++){
            if (temp.end >= intervals[i].start){
                if (intervals[i].end > temp.end){
                    temp.end = intervals[i].end;
                }
            }else{
                ans.push_back(temp);
                temp = intervals[i];
            }
        }
        ans.push_back(temp);
        return ans;
    }
};