我是Python新手。我编写了一个代码,用于快速排序以升序对整数进行排序。使用-Ubuntu 16.10和python3.5
代码-
import random
a=[]
n=int(input("Enter size :\n"))
for i in range(0,n):
a.append(int(random.randrange(0,100)))
print("Before Sorting:",a)
def quick(a,low,high):
if(low<high):
i=low
j=high
key=a[low]
flag=1
while (flag==1):
i += 1
while(a[i]<key):
i += 1
while (a[j]>key):
j -= 1
if (i<j):
a[i],a[j]=a[j],a[i]
else:
flag=0
a[low],a[j]=a[j],a[low]
quick(a,low,j-1)
quick(a,j+1,high)
# Calling function quick where a = List, 0 = Start Index ,n-1 = Last Index
quick(a,0,n-1)
print("After Sorting:",a)
当我运行代码时,它抛出IndexError:列表索引超出范围,但是如果我使用相同的输入来运行相同的代码,它将给出正确的输出。例如 -使用n = 5第一次运行代码
linux@linux-Lenovo-G50-30:~/PYTHON/practice/run1$ python3 quick.py
Enter size :
5
Before Sorting : [55, 23, 57, 86, 20]
Traceback (most recent call last):
File "quick.py", line 30, in <module>
quick(a,0,n-1)
File "quick.py", line 27, in quick
quick(a,j+1,high)
File "quick.py", line 17, in quick
while(a[i]<key):
IndexError: list index out of range
第二次以n = 5运行代码
Enter size :
5
Before Sorting : [6, 5, 93, 84, 32]
Traceback (most recent call last):
File "quick.py", line 30, in <module>
quick(a,0,n-1)
File "quick.py", line 27, in quick
quick(a,j+1,high)
File "quick.py", line 17, in quick
while(a[i]<key):
IndexError: list index out of range
第三次以n = 5运行代码
linux@linux-Lenovo-G50-30:~/PYTHON/practice/run1$ python3 quick.py
Enter size :
5
Before Sorting : [87, 18, 94, 1, 64]
After Sorting : [1, 18, 64, 87, 94]
我不知道为什么会这样。我正在使用Ubuntu 16.10和python3.5
您的代码有时起作用而有时不起作用的原因是,您正在建立一个随机数字数组。如您的帖子所示,即使使用相同的输入数据(列表长度),数字也每次都不同。您的quick()
功能适用于某些输入数据,而不适用于其他输入数据。之所以失败,是因为a[i]<key
假定i-1
中存在a
个元素,并且根据您的数据,有时没有。
import random
a=[]
n=int(input("Enter size :\n"))
for i in range(0,n):
a.append(int(random.randrange(0,100)))
print("Before Sorting:",a)
def sort(a):
less = []
equal = []
greater = []
if len(a) > 1:
pivot = a[0]
for x in a:
if x < pivot:
less.append(x)
if x == pivot:
equal.append(x)
if x > pivot:
greater.append(x)
return sort(less)+equal+sort(greater)
else:
return a
a = sort(a)
print("After Sorting:",a)