C++ 580ms solution sort first O(nlogn), then O(n) time, O(1) space

  • 2
    class Solution {
    static bool IntervalCompare(Interval &a, Interval &b){
        return (a.start<b.start);
    vector<Interval> merge(vector<Interval>& intervals) {
        int k=intervals.size();
        if (k<=1) return intervals;
        vector<Interval> res;
        for (int i=0;i<k-1;i++){
            if (intervals[i].end>=intervals[i+1].end) {
                intervals[i+1].end = intervals[i].end;
                intervals[i+1].start = intervals[i].start;
            else if (intervals[i].end>=intervals[i+1].start){
                intervals[i+1].start = intervals[i].start;
            else res.push_back(intervals[i]);
        return res;

  • 1

    Neat solution, but its not O(1) space as its not done in-place.

  • 0

    Besides the output res, there is no other extra space. If this is not O(1), then there is no O(1) solution for all problem return a vector.

  • 1

    I agree, but O(1) is reserved for in-place solutions in general. For this problem, there is no O(1) solution as you stated.

  • 0

    Saying "O(nlogn) first, then O(n)" doesn't make any sense.
    With the same logic, every solution to every problem can be stated in the form "O(...) first, then constant time"

  • 0

    @rmn The title accurately describes the time complexity of each major part of the codes. That is it.

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