Python in-place merge sort error: index out of range

Question

would anyone know why my in place merge sort is "index out of range" ?

I originally had my "low" at 0 but decided to do a +1 for each "low,mid,high" to compensate for index space. Can anyone find anything? Thanks.

def merge(array, low, mid, high):

    i,j,k = low,mid+1,low
    leftarray = array[low:mid+1]
    rightarray = array[mid+1:high+1]

    temp= [0]*high

    while i<=mid and j<=high:

        if array[i]<array[j]:
            temp[k] = array[i]
            i+=1
        else:
            temp[k] = array[j]
            j+=1
        k+=1

    if i>mid:
        temp[k:high+1] = array[j:high+1]
    else:
        temp[k:high+1] = array[i:mid+1]  

    array[low:high+1] = temp[low:high+1]

    def inplace(array,low,high):

        if low<high:
            mid = int((low+high)/2)
            inplace(array,low,mid)
            inplace(array,mid+1,high)
            merge_test(array,low,mid,high)


    array = [20,30,21,15,42,45,31,0,9]
    inplace(array, 0, len(array)-1)
    print(array)

Answer 1

• The error you have is in your code this part is incorrectly indented. It should be outside of while loop. Once merging is done. Refer to merge sort pseudo code to find where is the bug.

if i>mid:
    temp[k:high+1] = array[j:high+1]
else:
    temp[k:high+1] = array[i:mid+1]  

array[low:high+1] = temp[low:high+1]

• The following code is working.

def merge_test(array, low, mid, high):

    i,j,k = low,mid+1,low
    leftarray = array[low:mid+1]
    rightarray = array[mid+1:high+1]

    temp= [0]*high

    while i<=mid and j<=high:

        if array[i]<array[j]:
            temp[k] = array[i]
            i+=1
        else:
            temp[k] = array[j]
            j+=1
        k+=1


    if i>mid:
        temp[k:high+1] = array[j:high+1]
    else:
        temp[k:high+1] = array[i:mid+1]  

    array[low:high+1] = temp[low:high+1]


def inplace(array,low,high):

    if low<high:
        mid = int((low+high)/2)
        inplace(array,low,mid)
        inplace(array,mid+1,high)
        merge_test(array,low,mid,high)


array = [20,30,21,15,42,45,31,0,9]
inplace(array, 0, len(array)-1)
print(array)

output :

[0, 9, 15, 20, 21, 30, 31, 42, 45]

PS: please always post full error stack trace. It helps debugging code. You should also try reading stack trace.