python实现排序算法 python实现排序算法解析

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

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]

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

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

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)

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