爲什麼此代碼無法正確運行所有輸入？

Question

def quicksort(a,l,h): 
    if l>=h: 
     return 
    pivot = a[l] 
    i=l+1 
    for j in range(l+1,h+1): 
     if a[i]<pivot: 
      a[i],a[j] = a[j],a[i] 
      i+=1 
    a[l],a[i-1] = a[i-1],a[l] 
    quicksort(a,l,i-2) 
    quicksort(a,i,h) 


a = [6,7,8,9,5,1,2,3,4] 
print 'Before sort',a 
quicksort(a,0,len(a)-1) 
print 'After sort',a 

它適用於[9,8,7,6,5,4,3,2,1]但不適用於[6,7,8,9,5,1,2,3,4]

Answer 1

你寫這個的方式不是很Pythonic，更類似於你如何在C中做它。它是否需要進行就地操作？用返回值來做它似乎更清楚：

def quicksort(a): 
    if len(a) <= 1: 
     return a 

    bot = [] 
    eq = [] 
    top = [] 
    pivot = a[0] 

    for x in a: 
     if x < pivot: 
      bot.append(x) 
     elif x == pivot: 
      eq.append(x) 
     else: 
      top.append(x) 

    return quicksort(bot) + eq + quicksort(top)