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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].

Solution:

We can solve this by comparing the start of the next interval with the end of the current interval and merged if the start of the next interval is less than the end of the current interval.
For this we need to sort the interval based on the start of the intervals.

Note: Please try to solve it yourself before looking into the solution below

class Solution {
    public int[][] merge(int[][] intervals) {
        
        if(intervals.length<=1) return intervals;
        
        List<int[]> mergedIntervals = new ArrayList<>();
        
        Arrays.sort(intervals, (arr1, arr2) -> Integer.compare(arr1[0], arr2[0]));
        
        int[] currentInterval = intervals[0];
        
        mergedIntervals.add(currentInterval);
        
        for(int[] interval: intervals){
            int currentStart = currentInterval[0];
            int currentEnd = currentInterval[1];
            int newStart = interval[0];
            int newEnd = interval[1];
            
            if(currentEnd>=newStart){
                currentInterval[1] = Math.max(currentEnd, newEnd);
            }else{
                currentInterval = interval;
                mergedIntervals.add(currentInterval);
            }
            
        }
        
        
        return mergedIntervals.toArray(new int[mergedIntervals.size()][]);
    }
}