56. Merge Intervals

Given a collection of intervals, merge all overlapping intervals.

Example 1:

Input: [[1,3],[2,6],[8,10],[15,18]]
Output: [[1,6],[8,10],[15,18]]
Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].

Example 2:

Input: [[1,4],[4,5]]
Output: [[1,5]]
Explanation: Intervals [1,4] and [4,5] are considered overlapping.

對開始時間點sort。

vector<vector<int>> merge(vector<vector<int>>& intervals) { // time: O(nlogn); space: O(n)
    vector<vector<int> > res;
    if (intervals.empty()) return res;
    sort(intervals.begin(), intervals.end());
    for (vector<int>& interval : intervals) {
        if (res.empty() || res.back()[1] < interval[0]) {
            res.push_back(interval);
        } else {
            res.back()[1] = max(res.back()[1], interval[1]);
        }
    }
    return res;
}

57. Insert Interval