Python排序算法再理解

最新推荐文章于 2025-04-11 18:31:51 发布

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本文详细记录了使用 Python 语言实现的经典排序算法，包括冒泡排序、选择排序、插入排序、希尔排序和归并排序，并提供了算法的具体实现代码。

近几天，重新看了一些排序算法方面的资料，发现自己对排序算法的理解还有很多不足之处。所以重新用Python实现了一些排序算法。

现记录一下，以备日后查看。

主要算法实现思想详见Brad Miller 和 David Ranum的《Problem Solving with Algorithms and Data Structures》一书。

1. 冒泡排序

def bubble(alist):
	for i in range(len(alist) - 1, 0, -1):
		for j in range(i):
			if alist[j] > alist[j+1]:
				tmp = alist[j]
				alist[j] = alist[j+1]
				alist[j+1] = tmp

>>> alist = [random.randint(0, 100) for i in range(10)]
>>> alist
[96, 78, 84, 39, 72, 6, 33, 58, 43, 83]
>>> bubble(alist)
>>> alist
[6, 33, 39, 43, 58, 72, 78, 83, 84, 96]

2. 选择排序

def selection(alist):
	for i in range(len(alist)):
		for j in range(i+1, len(alist)):
			if alist[i] > alist[j]:
				tmp = alist[i]
				alist[i] = alist[j]
				alist[j] = tmp

>>> alist = [random.randint(0,100) for i in range(10)]
>>> alist
[64, 94, 19, 58, 9, 49, 100, 72, 42, 84]
>>> selection(alist)
>>> alist
[9, 19, 42, 49, 58, 64, 72, 84, 94, 100]

3. 插入排序

def insertion(alist):
	for i in range(1, len(alist)):
		cv = alist[i]
		j = i - 1
		while j >= 0 and alist[j] > cv:
			alist[j+1] = alist[j]
			j -= 1
		alist[j+1] = cv

>>> alist = [random.randint(0,100) for i in range(10)]
>>> alist
[72, 66, 58, 72, 58, 76, 62, 39, 75, 64]
>>> insertion(alist)
>>> alist
[39, 58, 58, 62, 64, 66, 72, 72, 75, 76]

4. 希尔排序

def incrInsert(alist, start, incr):
	for i in range(start+incr, len(alist), incr):
		cv = alist[i]
		j = i - incr
		while j >= 0 and alist[j] > cv:
			alist[j+incr] = alist[j]
			j -= incr
		alist[j+incr] = cv

def shell(alist):
	incr = len(alist) // 2
	while incr > 0:
		for start in range(incr):
			incrInsert(alist, start, incr)
		incr //= 2

>>> alist = [random.randint(0, 100) for i in range(10)]
>>> alist
[38, 65, 6, 97, 5, 9, 80, 84, 90, 0]
>>> shell(alist)
>>> alist
[0, 5, 6, 9, 38, 65, 80, 84, 90, 97]

5. 归并排序

def merge(alist):
	if len(alist) > 1:
		mid = len(alist) // 2
		left = alist[:mid]
		right = alist[mid:]
		merge(left)
		merge(right)
		i = 0
		j = 0
		k = 0
		while i < len(left) and j < len(right):
			if left[i] > right[j]:
				alist[k] = right[j]
				j += 1
			else:
				alist[k] = left[i]
				i += 1
			k += 1
		while i < len(left):
			alist[k] = left[i]
			i += 1
			k += 1
		while j < len(right):
			alist[k] = right[j]
			j += 1
			k += 1

>>> alist = [random.randint(0, 100) for i in range(10)]
>>> alist
[56, 99, 24, 19, 59, 32, 47, 97, 4, 31]
>>> merge(alist)
>>> alist
[4, 19, 24, 31, 32, 47, 56, 59, 97, 99]