class Solution {
public:
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        vector<vector<int>> vec_vec_int;
        sort(intervals.begin(), intervals.end());
        int left = 0, right = 1;
        int n = intervals.size();
        if(n == 0)
            return {};
        while(right < n){
            if(intervals[left][1] >= intervals[right][0]){
                intervals[left][0] = min(intervals[left][0], intervals[right][0]);
                intervals[left][1] = max(intervals[left][1], intervals[right][1]);
            }
            else{
                vec_vec_int.push_back(intervals[left]);
                left = right;
            }
            right++;
        }
        vec_vec_int.push_back(intervals[left]);
        return vec_vec_int;
    }
};

Accepted
168/168 cases passed (16 ms)
Your runtime beats 84.49 % of cpp submissions
Your memory usage beats 95.07 % of cpp submissions (13.7 MB)