def merge_sort(arr) :
    n = len(arr)
    if n <= 1 :
        return arr
    mid = n//2
    return merge(merge_sort(arr[:mid]), merge_sort(arr[mid:]))
 
def merge(arr1, arr2) :
    result = []
    while (len(arr1) > 0) and (len(arr2) > 0) :
        if arr1[0] < arr2[0] :
            result.append(arr1[0])
            arr1 = arr1[1:]
        else:
            result.append(arr2[0])
            arr2 = arr2[1:]
 
    result.extend(arr1)
    result.extend(arr2)
    return result
 
print(merge_sort([10,7,5,15,3,8,9,5,10,3,1]))

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