解答例
import random
def partition(array):
pivot = array[0]
left = [] # 小さいもの
pivots = [] # 同じ値のもの (自分自身も比較される)
right = [] # 大きいもの
for val in array:
if val < pivot:
left.append(val)
elif val == pivot:
pivots.append(val)
else:
right.append(val)
return(left + pivots + right)
a = [random.randint(0,100) for i in range(10)]
print("before = {}".format(a))
print("pivot = {}".format(a[0]))
print("after = {}".format(partition(a)))
<実行例>
tsuchiya@www1 python]$ python3 partition.py
before = [17, 42, 2, 75, 13, 3, 53, 61, 70, 51]
pivot = 17
after = [2, 13, 3, 17, 42, 75, 53, 61, 70, 51]
[tsuchiya@www1 python]$ python3 partition.py
before = [38, 74, 35, 12, 74, 30, 54, 24, 68, 50]
pivot = 38
after = [35, 12, 30, 24, 38, 74, 74, 54, 68, 50]