#leetcode 56 Merge Intervals

Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input.

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] overlap, 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.

Constraints:

• 1 <= intervals.length <= 104
• intervals[i].length == 2
• 0 <= starti <= endi <= 104

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class Solution {
    public int[][] merge(int[][] intervals) {
        List<int[]> res = new ArrayList<>();
        Arrays.sort(intervals, (a, b) -> a[0] - b[0]);
        int[] pre = intervals[0];
        for(int i = 1; i < intervals.length; i++) {
            if(intervals[i][0] > pre[1]) {
                res.add(pre);
                pre = intervals[i];
            }else{
                pre[1] = Math.max(pre[1], intervals[i][1]);
            }
        }
        res.add(pre);
        return res.toArray(new int[0][]);
    }
}