sortings in python

这篇主要写几种sort的方法，后面还会持续更新。

1. heapsort

heap sort uses an array as a full tree to sort.  time complexity is nlogn  space is O(1) because  it sorts in place.

it requires random access so we use array

everytime it sift down the largest element from the top.

code is as follow:

def siftdown(num,start,end):    root=start    while 2*root+1<=end:        child=2*root+1        if child+1<=end and num[child]<num[child+1]:            child+=1        if num[root]<num[child]:            num[root],num[child]=num[child],num[root]            root=child        else:            return

def heap(num):    count=(len(num)-2)/2    start=count #stat is the largest parent    while start>=0:# all nodes below the start index are in heap order        siftdown(num,start,len(num)-1)        start-=1# all nodes are in heap order    print num    for end in range(len(num)-1,0,-1):        num[end],num[0]=num[0],num[end]# swap the root with the last element        siftdown(num,0,end-1)# decrase the size of the heap so the previous max value will stay in its proper place    print num

 2. insertion sort:

O(n^2) O( 1)

每次都把第一个循环到的位置排列一遍

def insertion(num):    for i in range(1,len(num)):        j=i        while j>0 and num[j]>num[j-1]:            num[j],num[j-1]=num[j-1],num[j]            j-=1    print num

3.quick sort 

最差为O(n^2)

一般为nlogn

def quick(num,start,end):    if end-start>0:        pivot,left,right=num[start],start,end        while left<=right:            while num[left]<pivot:                left+=1            while num[right]>pivot:                right-=1            if left<=right:                num[left],num[right]=num[right],num[left]                left+=1                right-=1        quick(num,start,right)        quick(num,left,end)def quicksort(num):    quick(num,0,len(num)-1)    def main():    num=[3,1,9,0,8,7,2,10]    quicksort(num)    print numif __name__=="__main__":    main()

radix sort.

这种方法用的比较少，但是也是很重要的一种方法，时间复杂度取决于最大数的位数比如最大数是五位 的 那时间复杂度就是O(5*n)

def radix(num):    RADIX=10    maxlength=False    tmp,placement=-1,1    while not maxlength:        maxlength=True        bucket=[list() for _ in range(RADIX)]        for i in num:            tmp=i/placement            bucket[tmp%RADIX].append(i)            if maxlength and tmp>0:                maxlength=False                a=0        for i in range(RADIX):            buck=bucket[i]            for j in buck:                num[a]=j                a+=1        placement*=RADIX    return numdef main():    num=[28,1,22,10,9,30,8]    print radix(num)if __name__=="__main__":    main()