Given an array of intervals where intervals[i] = [start, end], merge all overlapping intervals.

Example 1:

Input:
1 3
2 6
8 10
15 18
Output:
1 6
8 10
15 18

Example 2:

Input:
1 4
4 5
Output:
1 5

Constraints:

• 1 ≤ intervals.length ≤ 10⁴
• intervals[i].length == 2
• 0 ≤ start ≤ end ≤ 10⁴

Input format: First line: number of intervals. Then each interval on its own line as "start end".

Output format: Merged intervals, one per line.