When I was solving the same TwoSum question on LeetCode, I once saw interesting approach - using the dictionary with the difference between “target” number and current number in a cycle being a key, and the index of that number - as a value.

Looks like that:

```
def find_sum(lst, k):
dicc = {}
for i in range(len(lst)):
ost = k - lst[i]
if ost not in dicc:
dicc[lst[i]] = i
else:
return [dicc[ost], i]
```

but the same approach (with different variable names) is correct for the leetcode problem, but gives wrong result here. Can’t understand why.

Course: https://www.educative.io/courses/data-structures-in-python

Lesson: Educative: Interactive Courses for Software Developers