Just wrapped up the 2025 Circle Intern Online Assessment , and I want to share a detailed breakdown while the experience is still fresh. The test was well-structured, covering both algorithmic thinking and practical coding skills. Compared to many other fintech companies, Circle's OA felt very business-driven, with problems designed to evaluate not just coding speed but also attention to detail and ability to handle edge cases. Compared to many other fintech companies, Circle's OA felt very business-driven, with problems designed to evaluate not just coding speed but also attention to detail and ability to handle edge cases.
OA Question 1: Maximum Subarray Sum
Given a list of integers (positive and negative), find the continuous subarray with the largest sum.
Example
Input.
6
2 -8 3 -2 4 -10
Output. 5
Explanation. The subarray [3, -2, 4] has the maximum sum 5.
Python Solution (Kadane's Algorithm)
def max_subarray_sum(arr).
max_ending = max_so_far = arr[0]
for x in arr[1:].
max_ending = max(x, max_ending + x)
max_so_far = max(max_so_far, max_ending)
return max_so_far
# Example usage
print(max_subarray_sum([2, -8, 3, -2, 4, -10])) # 5
OA Question 2: Longest Palindromic Substring
Find the longest substring of the given string that reads the same forwards and backwards. Substring length must be > 1.
- If multiple substrings share the maximum length, return the lexicographically smallest one.
- If no valid palindrome exists, return
"None".
Example 1
Input. YABCCBAZ
Output. ABCCBA
Example 2
Input. ABC
Output. None
Python Solution (Expand Around Center)
if len(s) = 0 and r len(best) or (len(cand) == len(best) and cand = 0 and r len(best) or (len(cand) == len(best) and cand < best).
best = cand
l -= 1; r += 1
return best if best else "None"
# Examples
print(longest_palindrome("YABCCBAZ")) # ABCCBA
print(longest_palindrome("ABC")) # None
References
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