Merge Sort
Implement merge sort: return a new array with the numbers of arr in ascending order, without using the built-in sort. Equal values must keep their relative order (stable).
mergeSort([9, 3, 6, 2, 1, 11]) -> [1, 2, 3, 6, 9, 11] mergeSort([]) -> []
Hints
Hint 1
Base case: zero or one element is sorted. Otherwise sort the two halves recursively and merge.
Hint 2
Merge with an index into each half, taking from the left on ties for stability, then append whatever remains.