### My issue

- What is the expected time complexity for this question?
- If less then O(n^2), someone please explain their approach… or

just hint like what is to be used?

I just can’t do better than O(n^2).

### My code

```
from collections import defaultdict as dd
n = int(input())
a = list(map(int,input().split()))
rights = dd(lambda:0)
lefts = [a[0]]
for i in range(1,n):
rights[a[i]] += 1
ans = 0
for i in range(1,n):
ele = a[i]
rights[ele] -= 1
for left in lefts:
if rights[2*ele-left] >= 1:
ans += rights[2*ele-left]
lefts.append(ele)
print(ans)
```

Problem Link: COUNTARI Problem - CodeChef