Python 3: Variable Scoping

Question

def max_sum_subarray(arr):
    cur_max_sum = global_max_sum = arr[0]
    start = end = 0

    sz = len(arr)
    for i in range(1, sz):
        cur_max_sum = max(arr[i], cur_max_sum+arr[i])
        global_max_sum = max(global_max_sum, cur_max_sum)
        if cur_max_sum > global_max_sum:
            global_max_sum = cur_max_sum
            end = i
    g = global_max_sum

    for i in range(end, -1, -1):
        g -= arr[i]
        if not g:
            start = i
            break

    ans = {
        'global_max_sum': global_max_sum,
        'start': start+1,
        'end': end+1
    }
    return ans

Here, start and end don't get updated inside for loop under if, though the condition satisfies. If start or end is used out of if, there is no problem with it. Is there any scoping problem or something else? Please explain me in details.

Thanks in advance.

Following How to debug small programs (#1) helps you find this kind of error. — Patrick Artner
– Patrick Artner, Commented Jul 22, 2018 at 20:10

Mr. Llama · Accepted Answer · 2018-07-22 20:04:11Z

3

It's a logic error:

global_max_sum = max(global_max_sum, cur_max_sum)
if cur_max_sum > global_max_sum:

There's literally no way for cur_max_sum to be greater than global_max_sum.

answered Jul 22, 2018 at 20:04

Mr. Llama

21k3 gold badges70 silver badges121 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

5hakir Over a year ago

I've transformed global_max_sum = max(global_max_sum, cur_max_sum) into if , but forgot to comment it. Thanks @Mr. Llama.

Collectives™ on Stack Overflow

Python 3: Variable Scoping

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related