python算法学习之桶排序算法实例(分块排序)

def insertion_sort(A):
"""插入排序，作为桶排序的子排序"""
n = len(A)
if n <= 1:
return A
B = [] # 结果列表
for a in A:
i = len(B)
while i > 0 and B[i-1] > a:
i = i - 1
B.insert(i, a);
return B

def bucket_sort(A):
"""桶排序，伪码如下：
BUCKET-SORT(A)
1 n ← length[A] // 桶数
2 for i ← 1 to n
3 do insert A[i] into list B[floor(nA[i])] // 将n个数分布到各个桶中
4 for i ← 0 to n-1
5 do sort list B[i] with insertion sort // 对各个桶中的数进行排序
6 concatenate the lists B[0],B[1],...,B[n-1] together in order // 依次串联各桶中的元素

桶排序假设输入由一个随机过程产生，该过程将元素均匀地分布在区间[0,1)上。
"""
n = len(A)
buckets = [[] for _ in xrange(n)] # n个空桶
for a in A:
buckets[int(n * a)].append(a)
B = []
for b in buckets:
B.extend(insertion_sort(b))
return B

if __name__ == '__main__':
from random import random
from timeit import Timer

items = [random() for _ in xrange(10000)]

def test_sorted():
print(items)
sorted_items = sorted(items)
print(sorted_items)

def test_bucket_sort():
print(items)
sorted_items = bucket_sort(items)
print(sorted_items)

test_methods = [test_sorted, test_bucket_sort]
for test in test_methods:
name = test.__name__ # test.func_name
t = Timer(name + '()', 'from __main__ import ' + name)
print(name + ' takes time : %f' % t.timeit(1))