[LintCode] Merge Intervals

Given a collection of intervals, merge all overlapping intervals.

Example

Given intervals => merged intervals:

[                     [
  [1, 3],               [1, 6],
  [2, 6],      =>       [8, 10],
  [8, 10],              [15, 18]
  [15, 18]            ]
]

Challenge

O(n log n) time and O(1) extra space.

/**
 * Definition of Interval:
 * classs Interval {
 *     int start, end;
 *     Interval(int start, int end) {
 *         this->start = start;
 *         this->end = end;
 *     }
 */
class Solution {
    static bool compFunc(const Interval &i1, const Interval& i2)
    {
        return i1.start < i2.start;
    }
public:
    vector<Interval> merge(vector<Interval> &intervals) {

        int size = intervals.size();
        vector<Interval> res;
        if(0 == size) return res;
        sort(intervals.begin(), intervals.end(), compFunc);
        
        res.push_back(intervals[0]);
        for(int i=1;i<size;i++)
        {
            if(!(res.back().start>intervals[i].end 
                || res.back().end < intervals[i].start)){
                res.back().start = min(res.back().start, intervals[i].start);
                res.back().end = max(res.back().end, intervals[i].end);
            }
            else{
                res.push_back(intervals[i]);
            }
        }
        return res;
    }
};