QuickSort

def quicksort(a):
    if len(a) <= 1:
        return a
    pivot = a[len(a) // 2]
    left = [x for x in a if x < pivot]
    middle = [x for x in a if x == pivot]
    right = [x for x in a if x > pivot]
    return quicksort(left) + middle + quicksort(right)

def quicksort(a, start, end):
    if start >= end:                    # No elements to sort
        return

    pivot = a[start]                    # Choose a pivot
    l, r = start + 1, end               # Sort a[start+1 ... end]
    while l <= r:                       # While there are elements left in the range
        if a[l] < pivot:                # if a[l] < pivot => leave a[i] untouched
            l += 1                      # Increase the left pointer
        else:                           # otherwise move a[l] to the end
            a[l], a[r] = a[r], a[l]     # Swap a[l] and a[r] -> move to the end
            r -= 1                      # Reduce the right pointer

    a[start], a[r] = a[r], a[start]     # Swap pivot with a[r]
    quicksort(a, start, r - 1)          # Sort a[start ... r-1]
    quicksort(a, r + 1, end)            # Sort a[r+1 ... end]