56. Merge Intervals

https://leetcode.com/problems/merge-intervals/

Problem

Given a collection of intervals, merge all overlapping intervals.

Example 1:

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

NOTE: input types have been changed on April 15, 2019. Please reset to default code definition to get new method signature.

Constraints:

• intervals[i][0] <= intervals[i][1]

Solution

class Solution {
public:
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        if (intervals.empty()) return intervals;
        auto comparator = [](const auto &a, const auto &b) {
            if (a[0] != b[0]) return a[0] < b[0];
            else return a[1] < b[1];
        };
        sort(intervals.begin(), intervals.end(), comparator);
        vector<vector<int>> merged; merged.reserve(intervals.size());
        merged.push_back(intervals[0]);
        for (int i = 1; i < intervals.size(); ++i) {
            const int end = merged.back()[1];
            const int start = intervals[i][0];
            if (start <= end) {
                merged.back()[1] = max(end, intervals[i][1]); 
            } else {
                merged.push_back(intervals[i]);
            }
        }
        return merged;
    }
};

• #interval