[LC] 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.

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

class Solution {
    public int[][] merge(int[][] intervals) {
        List<int[]> res = new ArrayList<>();
        if (intervals.length == 0) {
            return new int[][] {};
        }
        Arrays.sort(intervals, (a, b) -> (a[0] - b[0]));
        int start = intervals[0][0];
        int end = intervals[0][1];
        for (int[] interval: intervals) {
            if (interval[0] <= end) {
                end = Math.max(end, interval[1]);
            } else {
                res.add(new int[]{start, end});
                start = interval[0];
                end = interval[1];
            }
        }
        // need to add back the last tuple
        res.add(new int[]{start, end});
        return res.toArray(new int[][] {});
    }
}