Homework-1/qselect.py

import random

def qselect(i, xs):
    if xs == []: return None

    pivot = xs.pop(random.randrange(len(xs)))
    left = [x for x in xs if x < pivot]
    right = [x for x in xs if x >= pivot]

    if i > len(left) + 1:
        return qselect(i - len(left) - 1, right)
    elif i == len(left) + 1:
        return pivot
    else:
        return qselect(i, left)