快速排序

平均时间复杂度为O(nlogn)，非稳定排序。实现如下：

def quick_sort(data):
    res = [val for val in data]
    print res
    quick_sort_imp(res, 0, len(data) - 1)
    return res


def quick_sort_imp(data, start, end):
    if start < end:
        index = partition(data, start, end)
        quick_sort_imp(data, start, index - 1)
        quick_sort_imp(data, index + 1, end)


def partition(data, start, end):
    left, right = start, end
    pivot = data[left]
    while left < right:
        while left < right and data[right] >= pivot:
            right -= 1
        data[left] = data[right]
        while left < right and data[left] <= pivot:
            left += 1
        data[right] = data[left]
    data[left] = pivot
    return left


if __name__ == '__main__':
    data = [1, 2, 3, 2, 2, 2, 5, 4, 2]
    print quick_sort(data)
    data = [5, 7, 21, 3, 4, 55, 6]
    print quick_sort(data)