python实现排序算法

一、冒泡排序

def bububle_sort(alist):
"""冒泡排序(稳定|n^2m)"""
    n = len(alist)
for j in range(n-1):
        count = 0
for i in range(0,n-1-j):
if alist[i]>alist[i+1]:
                count +=1
                alist[i], alist[i+1] = alist[i+1], alist[i]
if count==0:
return

二、选择排序

def select_sort(alist):
"""选择排序(不稳定|n^2)"""
    n = len(alist)
for j in range(n-1):
        min_index = j
for i in range(j+1,n):
if alist[min_index] > alist[i]:
                min_index = i
        alist[j], alist[min_index] = alist[min_index], alist[j]

三、插入排序

def insert_sort(alist):
"""插入排序(稳定|n^2)"""
    n = len(alist)
for j in range(1,n):
        i = j
while i>0:
if alist[i] < alist[i-1]:
                alist[i], alist[i-1] = alist[i-1], alist[i]
                i -= 1
else:
break 

四、希尔排序

def shell_sort(alist):
"""希尔排序(不稳定|n^2)"""
    n = len(alist)
    gap = n//2

while gap>=1:
for j in range(gap,n):
            i=j
while i>0:
if alist[i]<alist[i-gap]:
                    alist[i], alist[i-gap] = alist[i-gap], alist[i]
                    i -= gap
else:
break
        gap //=2

五、快速排序

def quick_sort(alist, first, last):
"""快速排序(不稳定|n^2)"""
if first >= last:
return
    mid_value = alist[first]
    low = first
    high = last
while low < high:
#high左移
while low <high and alist[high] >= mid_value:
            high -= 1
        alist[low] = alist[high]
#low右移
while low < high and alist[low] < mid_value:
            low += 1
        alist[high] =alist[low]  
#从循环退出时，low=high
    alist[low] = mid_value

#对low左边的列表执行快速排序
    quick_sort(alist, first, low-1)
#对low右边的列表执行快速排序
    quick_sort(alist, low+1, last)

六、归并排序

def merge_sort(alist):
"""归并排序(稳定|nlgn)"""
    n = len(alist)
if n <= 1:
return alist
    mid = n//2

#left 采用归并排序后形成新的有序列表
    left_li = merge_sort(alist[:mid])
#right 采用归并排序后形成新的有序列表
    right_li = merge_sort(alist[mid:])

#merge(left, right) 将两个有序的子序列合并为一个新的整体
    left_pointer, right_pointer = 0, 0
    result = []

while left_pointer < len(left_li) and right_pointer<len(right_li):
if left_li[left_pointer] < right_li[right_pointer]:
            result.append(left_li[left_pointer])
            left_pointer += 1
else:
            result.append(right_li[right_pointer])
            right_pointer += 1

    result += left_li[left_pointer:]
    result += right_li[right_pointer:]
return result