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].

Analyse: First sort, then merge. 

Notice the static function!

Runtime: 592ms

/**
 * 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(Interval &interval1, Interval &interval2){
        return interval1.start < interval2.start;
    }
    vector<Interval> merge(vector<Interval>& intervals) {
        vector<Interval> result;
        if(intervals.size() == 0) return result;
        if(intervals.size() == 1) return intervals;
        
        sort(intervals.begin(), intervals.end(), Solution::compare);
        Interval inter(intervals[0].start, intervals[0].end);
        for(int i = 1; i < intervals.size(); i++){
            if(inter.end < intervals[i].start){
                result.push_back(inter);
                inter.start = intervals[i].start;
                inter.end = intervals[i].end;
            }
            else{
                inter.start = min(inter.start, intervals[i].start);
                inter.end = max(inter.end, intervals[i].end);
            }
        }
        result.push_back(inter);
        return result;
    }
};

Runtime: 596ms.

/**
 * 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:
    vector<Interval> merge(vector<Interval>& intervals) {
        vector<Interval> result;
        if(intervals.empty()) return result;
        
        sort(intervals.begin(), intervals.end(), comp);
        result.push_back(intervals[0]);
        if(intervals.size() == 1) return result;
        
        for(int i = 1; i < intervals.size(); i++){
            if(intervals[i].start > result[result.size() - 1].end)
                result.push_back(intervals[i]);
            else{
                intervals[i].start = min(intervals[i].start, result[result.size() - 1].start);
                intervals[i].end = max(intervals[i].end, result[result.size() - 1].end);
                result.pop_back();
                result.push_back(intervals[i]);
            }
        }
        return result;
    }
    
    static bool comp(Interval int1, Interval int2){
        return int1.start < int2.start;
    }
};