Merge Intervalsmedium

/**
 * @param {number[][]} intervals
 * @return {number[][]}
 */
function merge(intervals) {
    // TODO: sort by start, then merge overlapping intervals
    return [];
}

console.log(merge([[1,3],[2,6],[8,10],[15,18]])); // [[1,6],[8,10],[15,18]]
console.log(merge([[1,4],[4,5]]));                 // [[1,5]]