# 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]

```
var merge = function(intervals) {
if(intervals.length <= 1) return intervals;
// sort the array so earlier start times are at the beginning
intervals = intervals.sort((a,b) => a[0] - b[0])
let output = [intervals[0]];
let current = output[0];
// If the current interval's end time is greater than or equal
// to the next interval's start time, then we know there is an
// overlap and we merge them.
// If there is no overlap, then we add the next interval to the
// list of intervals in our output array and repeat the process
// until we go through the entire list of intervals.
for(let i = 1; i< intervals.length;i++) {
const next = intervals[i]
if(current[1] >= next[0]) {
current[1] = Math.max(current[1], next[1]);
} else {
current = next;
output.push(current);
}
}
return output;
};
```

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