merge-intervals 合并区间

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].

合并有重叠的区间，且原区间序列无序

/**
 * Definition for an interval.
 * struct Interval {
 *     int start;
 *     int end;
 *     Interval() : start(0), end(0) {}
 *     Interval(int s, int e) : start(s), end(e) {}
 * };
 */
class Solution {
public:
    static bool compare(const Interval &first,const Interval &second)
    {
        if(first.start==second.start)
            return first.end<second.end;
        else
            return first.start<second.start;
    }
    vector<Interval> merge(vector<Interval> &intervals) {
        vector<Interval> ret;
        int n=intervals.size();
        int pre=, cur=;
        sort(intervals.begin(),intervals.end(),compare);
        while(cur<n)
        {
            while(cur<n&&intervals[pre].end>=intervals[cur].start)
            {
                intervals[pre].start=min(intervals[pre].start,intervals[cur].start);
                intervals[pre].end=max(intervals[pre].end,intervals[cur].end);
                cur++;
            }
            ret.push_back(intervals[pre]);
            pre=cur;

        }
        return ret;
    }
};