Python编程中归并排序算法的实现步骤详解

[6,2,3,1,7]

[6],[2],[3],[1],[7]

[2,6],[1,3],[7]

 a = [2,6] b = [1,3] c = [] 

a = [2,6] b = [3] c = [1] 

a = [6] b = [3] c = [1,2] 

a = [6] b = [] c = [1,2,3] 

a = [] b = [] c = [1,2,3,6]

[1,2,3,6,7]

#! /usr/bin/env python
#coding:utf-8

def merge_sort(seq):
 if len(seq) ==1:
 return seq
 else:
 middle = len(seq)/2
 left = merge_sort(seq[:middle])
 right = merge_sort(seq[middle:])

 i = 0 #left 计数
 j = 0 #right 计数
 k = 0 #总计数

 while i < len(left) and j < len(right):
  if left[i] < right [j]:
  seq[k] = left[i]
  i +=1
  k +=1
  else:
  seq[k] = right[j]
  j +=1
  k +=1

 remain = left if i<j else right
 r = i if remain ==left else j

 while r<len(remain):
  seq[k] = remain[r]
  r +=1
  k +=1

 return seq

#! /usr/bin/env python
#coding:utf-8


def merge_sort(lst): #此方法来自维基百科

 if len(lst) <= 1:
 return lst

 def merge(left, right):
 merged = []

 while left and right:
  merged.append(left.pop(0) if left[0] <= right[0] else right.pop(0))

 while left:
  merged.append(left.pop(0))

 while right:
  merged.append(right.pop(0))

 return merged

 middle = int(len(lst) / 2) 
 left = merge_sort(lst[:middle])
 right = merge_sort(lst[middle:])
 return merge(left, right)

#! /usr/bin/env python
#coding:utf-8


from heapq import merge

def merge_sort(seq):
 if len(seq) <= 1:
 return m
 else:  
 middle = len(seq)/2
 left = merge_sort(seq[:middle])
 right = merge_sort(seq[middle:])
 return list(merge(left, right))  #heapq.merge()

if __name__=="__main__":
 seq = [1,3,6,2,4]
 print merge_sort(seq)