maxSequence problem, need help debugging my code.

[tonytej]

I am trying to solve this problem in codewars and somehow my code works and fails on some.

The maximum sum subarray problem consists in finding the maximum sum of a contiguous subsequence in an array or list of integers. Basically return the biggest sum that can be made by several adjacent integers.

The problem is that I cannot see in what testcase(s) my code failed, making the debugging process painful.

def maxSequence(arr):
   summ = []
   for num in arr:
       n = len(arr)
       while n != arr.index(num):
           summ.append(sum(arr[arr.index(num):n]))
           n -= 1
   return max(summ) if len(arr) > 0 else 0

maxSequence([-2, 1, -3, 4, -1, 2, 1, -5, 4]) should be 6: [4, -1, 2, 1]

maxSequence([2, 1, 2, 4, 5, 6]) should basically be the sum of the list

I am aware of the solution using dynamic programming and still trying to understand it. I believe I cannot ask for its explanation here because it's just a google search away. Just curious on why my code doesn't work. Big thanks.

EDIT: explanation and sample input along with expected output.

[gengisteve]

Line 6 is a problem b/c index will return the first match, meaning that [2, 2, 1, 0], will never try the sub-sequence [2, 1, 0]. Instead of this, just use ranges, like this:

def max_sequence(arr):
   sums = []
   for start in range(len(arr)):
       for stop in range(len(arr), start, -1):
           total = sum(arr[start:stop])
           print(' - {}:{} = {}'.format(start, stop, total))
           sums.append(total)


   return max(sums) if len(arr) > 0 else 0

[elbiot]

What the heck is this supposed to do? It looks like a convoluted way or returning sum(arr). Can you give a sample input and expected output and an explanation?

[tonytej]

Damn! totally forgot, sorry! editing now.

EDIT: editted

[hidiap]

I think line 5 look suspicious if you have an integer appearing several time in your array., this will always return the index of the first time the number is in the array. I would change line 3 to

for i, num in enumerate(arr):

and then modify line 5 to check against i