Merge Intervals 运行比较快

class Solution {
public:
static bool cmp(Interval &a,Interval &b)
{
    return a.start<b.start;
}
    vector<Interval> merge(vector<Interval>& intervals) {
        vector<Interval> res;
        if(intervals.size()==0)return res;
        sort(intervals.begin(),intervals.end(),cmp);
        int i=1;
        int first=0;
        int j=first;
        Interval tmpin;
        while(i<intervals.size()){
            //第一种情况比如：[1,2] [3,4]
        if(intervals[i].start>intervals[j].end){tmpin.start=intervals[first].start;tmpin.end=intervals[j].end;res.push_back(tmpin);
            first=i;
            j=first;
            i=i+1;
        }
        
        //第二种  比如： [2,6] [3,7]
        else if(intervals[i].start<=intervals[j].end&&intervals[i].end>intervals[j].end)
        {
            i++;
            j=i-1;
        }
        //第三种  比如： [2,6] [1,3] 
        else
        {
           i++; 
        }
        
        }
        if(intervals[j].end>=intervals[i-1].end) {tmpin.start=intervals[first].start;tmpin.end=intervals[j].end;res.push_back(tmpin);}
        else{tmpin.start=intervals[first].start;tmpin.end=intervals[i-1].end;res.push_back(tmpin);}
        return res;
    }
};