python - 这个快排哪儿有问题？

Question

#coding=utf-8
import random

ls = [random.randint(1,20) for i in range(30)]

def quick_sort(li):
    if len(li) <=10:
        li.sort()
        return li
    lenth = len(li)
    if li[0]>li[lenth / 2]:
        li[lenth / 2], li[0] = li[0], li[lenth / 2]
    if li[0] > li[lenth-1]:
        li[lenth-1], li[0] = li[0], li[lenth-1]
    if li[lenth/2]>li[lenth-1]:
        li[lenth-1], li[lenth/2] = li[lenth/2], li[lenth-1]

    li[lenth/2], li[lenth-1] = li[lenth-1], li[lenth/2]
    i,j = 0 ,lenth-2
    while 1:
        while li[i]<=li[lenth-1] and i<lenth-2:
            i = i+1
        while li[j] > li[lenth-1] and j >= i:
            j = j-1
        if i>=j:
            break
        else:
            li[i], li[j] = li[j], li[i]
    li[i+1], li[lenth-1] = li[lenth-1], li[i+1]
    li = quick_sort(li[:i]) + quick_sort(li[i:])
    return li

if __name__ == '__main__':
    print quick_sort(ls)

Answer 1

二分排序，给你php版的，你用python照着改：

二分排序：
function quickSort($left,$right,$arr){
     $l=$left;
     $r=$right;
     $pivot=$arr[($left+$right)/2];
     while($l<$r){
          while ($arr[$l]<$pivot) $l++;
          while ($arr[$r]>$pivot) $r++;
          if($l>=$r) break;
          $temp=$arr[$l];
          $arr[$l]=$arr[$r];
          $arr[$r]=$temp;
          if($arr[$l]==$pivot) --$r;
          if($arr[$r]==$pivot)  ++$l;
     }
     if($l==$r){
          $l++;
          $r--;
     }
     if($left<$r) quickSort($left,$r,$arr);
     if($right>$i) quickSort($l, $right, $arr);
     return $arr;
}
$arr=array(0,5,-1,20,-20,45,32,-100,-200);
$test=quickSort(0,count($arr)-1,$arr);
print_r($test);

Answer 2

我不是很喜欢可以用递归的强行用while循环来写，要换成循环就干脆换成迭代的。
英文必应搜索quick sort python给的样例：

#Quick Sort
def quicksort(arr,i,j):
    if i<j:
        pos=partition(arr,i,j)
        quicksort(arr,i,pos-1)
        quicksort(arr,pos+1,j)

def partition(arr,i,j):
    pivot=arr[j]
    small=i-1
    for k in range(i,j):
        if arr[k]<=pivot:
            small+=1
            swap(arr,k,small)
    
    swap(arr,j,small+1)
    print "Pivot= "+str(arr[small+1])
    print arr
    return small+1
def swap(arr,i,j):
    temp=arr[i]
    arr[i]=arr[j]
    arr[j]=temp

arr=[9,4,8,3,1,2,5]
print "Initial Array :"+str(arr)  
quicksort(arr,0,len(arr)-1)