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].

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

//方法：先sort，然後再考慮情況合並。復雜度：O(nlogn)
class Solution {
public:
    struct compare {
        bool operator()( const Interval& a , const Interval& b) const {
            if( a.start==b.start) 
                return a.end < b.end;
            else 
                return a.start < b.start;
        }
    };

	vector merge(vector &intervals) {
	    if(intervals.size()==0)
	        return vector();
	    sort(intervals.begin() , intervals.end() , compare());
	    vector ans;
	    Interval temp;
	    temp = intervals[0];
	    for(int i=1; i