Python实现的几个常用排序算法实例

前段时间为准备百度面试恶补的东西，虽然最后还是被刷了，还是把那几天的“战利品”放点上来，算法一直是自己比较薄弱的地方，以后还要更加努力啊。

下面用python实现了几个常用的排序，如快速排序，选择排序，以及二路并归排序等等。

#encoding=utf-8
import random
from copy import copy

def directinsertsort(seq):
 """ 直接插入排序 """
 size = len(seq)
 for i in range(1,size):
  tmp, j = seq[i], i
  while j > 0 and tmp < seq[j-1]:
   seq[j], j = seq[j-1], j-1
  seq[j] = tmp
 return seq

def directselectsort(seq):
 """ 直接选择排序 """
 size = len(seq)
 for i in range(0,size - 1):
  k = i;j = i+1
  while j < size:
   if seq[j] < seq[k]:
    k = j
   j += 1
  seq[i],seq[k] = seq[k],seq[i]
 return seq

def bubblesort(seq):
 """冒泡排序"""
 size = len(seq)
 for i in range(1,size):
  for j in range(0,size-i):
   if seq[j+1] < seq[j]:
    seq[j+1],seq[j] = seq[j],seq[j+1]
 return seq

def _divide(seq, low, high):
 """快速排序划分函数"""
 tmp = seq[low]
 while low != high:
  while low < high and seq[high] >= tmp: high -= 1
  if low < high:
   seq[low] = seq[high]
   low += 1
  while low < high and seq[low] <= tmp: low += 1
  if low < high:
   seq[high] = seq[low]
   high -= 1
 seq[low] = tmp
 return low

def _quicksort(seq, low, high):
 """快速排序辅助函数"""
 if low >= high: return
 mid = _divide(seq, low, high)
 _quicksort(seq, low, mid - 1)
 _quicksort(seq, mid + 1, high)

def quicksort(seq):
 """快速排序包裹函数"""
 size = len(seq)
 _quicksort(seq, 0, size - 1)
 return seq

def merge(seq, left, mid, right):
 tmp = []
 i, j = left, mid
 while i < mid and j <= right:
  if seq[i] < seq[j]:
   tmp.append(seq[i])
   i += 1
  else:
   tmp.append(seq[j])
   j += 1
 if i < mid: tmp.extend(seq[i:])
 if j <= right: tmp.extend(seq[j:])

 seq[left:right+1] = tmp[0:right-left+1]

def _mergesort(seq, left, right):
 if left == right:
  return
 else:
  mid = (left + right) / 2
  _mergesort(seq, left, mid)
  _mergesort(seq, mid + 1, right)
  merge(seq, left, mid+1, right)

#二路并归排序
def mergesort(seq):
 size = len(seq)
 _mergesort(seq, 0, size - 1)
 return seq

if __name__ == '__main__':
 s = [random.randint(0,100) for i in range(0,20)]
 print s
 print "\n"
 print directselectsort(copy(s))
 print directinsertsort(copy(s))
 print bubblesort(copy(s))
 print quicksort(copy(s))
 print mergesort(copy(s))

运行结果如下：

e:\python_project\practice>sorting.py
[10, 47, 56, 76, 64, 84, 26, 8, 47, 51, 88, 81, 32, 95, 91, 29, 28, 69, 61, 45]

[8, 10, 26, 28, 29, 32, 45, 47, 47, 51, 56, 61, 64, 69, 76, 81, 84, 88, 91, 95]
[8, 10, 26, 28, 29, 32, 45, 47, 47, 51, 56, 61, 64, 69, 76, 81, 84, 88, 91, 95]
[8, 10, 26, 28, 29, 32, 45, 47, 47, 51, 56, 61, 64, 69, 76, 81, 84, 88, 91, 95]
[8, 10, 26, 28, 29, 32, 45, 47, 47, 51, 56, 61, 64, 69, 76, 81, 84, 88, 91, 95]
[8, 10, 26, 28, 29, 32, 45, 47, 47, 51, 56, 61, 64, 69, 76, 81, 84, 88, 91, 95]