常用排序算法的Python实现
最近一段时间学习了python，发现python真是个强大，强大到和Matlab相媲美。为了熟悉python，将之前的各种排序算法用python实现了一下。
常用的时间复杂度为O(n^2)的排序算法有冒泡排序，插入排序和选择排序，时间复杂度为O(nlog2(n))的算法有快速排序，归并排序和堆排序，
这里的快速排序的初始比较值partition是随机给定的，在用python进行编写时能更清楚的理解整个排序算法的过程。
1 import random 2 def BubbleSort(num): 3 n=len(num) 4 for i in range(0,n): 5 for j in range(i,n): 6 if num[i]>=num[j]: 7 num[i],num[j]=num[j],num[i] 8 return num 9 def SelectSort(num): 10 for i in range(0,len(num)): 11 mindex=i 12 for j in range(i,len(num)): 13 if num[mindex]>num[j]: 14 mindex=j 15 num[mindex],num[i]=num[i],num[mindex] 16 return num 17 def InsertSort(num): 18 for i in range(1,len(num)): 19 j=i-1 20 tmp=num[i] 21 while j>0 and tmp<num[j]: 22 num[j+1]=num[j] 23 j-=1 24 num[j]=tmp 25 return num 26 def MergerSort(num): 27 if len(num)<=1: 28 return num 29 left=MergerSort(num[:len(num)/2]) 30 right=MergerSort(num[len(num)/2:]) 31 result=[] 32 while len(left)>0 and len(right)>0: 33 if left[0]>right[0]: 34 result.append(right.pop(0)) 35 else: 36 result.append(left.pop(0)) 37 if len(left)>0: 38 result.extend(MergerSort(left)) 39 else: 40 result.extend(MergerSort(right)) 41 return result 42 def QuickSort(num): 43 if len(num)<=1: 44 return num 45 greater=[] 46 less=[] 47 p=num.pop(random.randint(0,len(num)-1)) 48 for item in num: 49 if item < p: 50 less.append(item) 51 else: 52 greater.append(item) 53 return QuickSort(less)+[p]+QuickSort(greater) 54 ############################################################ 55 def InsertIntoHeap(x,heap): 56 if len(heap)==0: 57 heap=[x] 58 return heap 59 heap.append(x) 60 pos=len(heap) 61 while True: 62 if pos==1: 63 return heap 64 father=pos/2 65 if heap[father-1]<heap[pos-1]: 66 heap[father-1],heap[pos-1]=heap[pos-1],heap[father-1] 67 pos=father 68 else: 69 return heap 70 def CreateHeap(x): 71 b=[] 72 for i in x: 73 InsertIntoHeap(i,b) 74 return b 75 def HandHeap(a): 76 if a==None or type(a)!=list: 77 return 78 if a==[] or len(a)==1: 79 return a 80 pos=0 81 while True: 82 if 2*(pos+1)>len(a): 83 return a 84 if 2*(pos+1)==len(a): 85 if a[pos]<a[2*pos+1]: 86 a[pos],a[2*pos+1]=a[2*pos+1],a[pos] 87 return a 88 if 2*(pos+1)+1<=len(a): 89 if a[pos]<a[2*pos+1]and a[2*pos+1]>=a[2*pos+2]: 90 a[pos],a[2*pos+1]=a[2*pos+1],a[pos] 91 pos=2*pos+1 92 elif a[pos]<a[2*pos+2]and a[2*pos+1]<a[2*pos+2]: 93 a[pos],a[2*pos+2]=a[2*pos+2],a[pos] 94 pos=2*pos+2 95 else: 96 return a 97 def HeapSort(num): 98 if num==None or type(num)!=list: 99 return 100 b=CreateHeap(num) 101 a=[] 102 while b: 103 a.append(b[0]) 104 b[0]=b[len(b)-1] 105 b.pop() 106 b=HandHeap(b) 107 return a 108
接下来学习python的面向对象编程。
