[英]Implementing Merge Sort in Python
I'm trying to implement simple merge sort algorithm in Python.我正在尝试在 Python 中实现简单的合并排序算法。
arr=[1,3,5,2,4,6]
n=6
l=0
h=n-1
def merge_Sort(l,h):
if(l==h):
return arr[l]
m=(h+l)//2
arr1=merge_Sort(l,m)
arr2=merge_Sort(m+1,h)
s1=m-l
s2=h-(m+1)
mer=[]
k1=k2=0
while(k1<=s1 or k2<=s2):
if(arr1[k1] < arr2[k2]):
mer.append(arr1[k1])
k1+=1
else:
mer.append(arr2[k2])
k2+=1
if(k1>s1):
while(k2<=s2):
mer.append(arr2[k2])
k2+=1
if(k2>s2):
while(k1<=s1):
mer.append(arr1[k1])
k1+=1
return mer
res=merge_Sort(l,h)
print(res)
But I'm getting this error message when running the above code:但是在运行上述代码时我收到此错误消息:
TypeError: 'int' object is not subscriptable
类型错误:“int”对象不可下标
Can anybody explain to me why I'm geting this error?任何人都可以向我解释为什么我会收到此错误?
The problems are here:问题在这里:
if(l==h):
return arr[l]
...
while(k1<=s1 or k2<=s2):
Use this code instead:请改用此代码:
if(l==h):
return arr[l:l+1]
...
while(k1<=s1 and k2<=s2):
Side note, this piece of code:旁注,这段代码:
if(k1>s1):
while(k2<=s2):
mer.append(arr2[k2])
k2+=1
if(k2>s2):
while(k1<=s1):
mer.append(arr1[k1])
k1+=1
can be simplified to this:可以简化为:
mer.extend(arr1[k1:s1+1])
mer.extend(arr2[k2:s2+1])
Change this:改变这个:
if(l==h):
return arr[l]
into:进入:
if(l==h):
return [arr[l]]
and this:和这个:
while(k1<=s1 or k2<=s2):
into:进入:
while(k1<=s1 and k2<=s2):
I tested it and it works fine.我测试了它,它工作正常。
TypeError: 'int' object is not subscriptable
means you're trying to iterate (or use something like a[0]
) over int
. TypeError: 'int' object is not subscriptable
意味着您正在尝试在int
上迭代(或使用类似a[0]
东西)。
Add this before the "crash line".在“崩溃线”之前添加它。
print(arr1, arr2)
Output: 1 3
输出:
1 3
So you're doing 3[k2]
.所以你在做
3[k2]
。
an alternative method would be :另一种方法是:
def merge_sort(a): def merge_sort(a):
if len(a) <= 1:
return a
mid = len(a) // 2
left = merge_sort(a[:mid])
right = merge_sort(a[mid:])
return merge(left, right)
def merge(left,right):定义合并(左,右):
if not left:
return right
if not right:
return left
if left[0] < right[0]:
return [left[0]] + merge(left[1:], right)
return [right[0]] + merge(left, right[1:])
This would be a relatively standard method:这将是一个相对标准的方法:
def merge(left, right):
res = []
while len(left) > 0 and len(right) > 0:
if left[0] <= right[0]:
res.append(left[0])
left.pop(0)
else:
res.append(right[0])
right.pop(0)
while len(left) > 0:
res.append(left[0])
left.pop(0)
while len(right) > 0:
res.append(right[0])
right.pop(0)
return res
def merge_sort(lst):
if len(lst) <= 1:
return lst
left = lst[:(len(lst)//2)]
right = lst[(len(lst)//2):]
left = merge_sort(left)
right = merge_sort(right)
return merge(left,right)
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