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x0lg0n merged 1 commit into from
Oct 27, 2025
Merged

Add unique number finder script with input parsing #126

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66 changes: 66 additions & 0 deletions Python/uniqueNo.py
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Original file line number Diff line number Diff line change
@@ -0,0 +1,66 @@

"""
uniqueNo.py

Find the unique number in an array where every other element appears exactly twice.

Input (stdin):
- First line: optional integer n (number of elements)
- Remaining tokens: integers (either n integers, or a list of integers)

Output:
- Prints the unique integer (the one that appears once) to stdout.

If no input is provided, a small demo runs.
"""

import sys
from typing import Iterable


def unique_number(arr: Iterable[int]) -> int:
"""Return the unique number when every other number appears exactly twice.

This uses XOR properties: x ^ x = 0 and x ^ 0 = x, so XORing all numbers
leaves the unique value.
"""
res = 0
for x in arr:
res ^= x
return res


def parse_input(stream) -> list:
data = stream.read().strip().split()
if not data:
return []
try:
nums = [int(tok) for tok in data]
except ValueError:
raise

# If first token is count and matches remaining length, skip it
if len(nums) >= 2 and nums[0] == len(nums) - 1:
return nums[1:]
Comment on lines +43 to +44
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@coderabbitai coderabbitai bot Oct 27, 2025

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⚠️ Potential issue | 🔴 Critical

Critical bug: ambiguous count detection can remove the unique number.

The heuristic nums[0] == len(nums) - 1 cannot reliably distinguish between a count prefix and an actual array element. This causes incorrect results when the unique number happens to be the first element AND equals len(nums) - 1.

Example failure case:

  • Input: 5 1 2 3 1 2 (no count, unique number is 5)
  • After parsing: nums = [5, 1, 2, 3, 1, 2]
  • Condition: nums[0] (5) == len(nums) - 1 (5) → True
  • Result: skips first element → [1, 2, 3, 1, 2] → returns 3 (incorrect, should be 5)

Recommended fix: Remove the ambiguity by requiring a consistent input format. Choose one of:

  1. Always require a count prefix:
 def parse_input(stream) -> list:
 	data = stream.read().strip().split()
-	if not data:
+	if len(data) < 2:
 		return []
 	try:
 		nums = [int(tok) for tok in data]
 	except ValueError:
 		raise
 
-	# If first token is count and matches remaining length, skip it
-	if len(nums) >= 2 and nums[0] == len(nums) - 1:
-		return nums[1:]
-	return nums
+	# Always treat first token as count
+	count = nums[0]
+	if count != len(nums) - 1:
+		raise ValueError(f"Count mismatch: expected {count} elements, got {len(nums) - 1}")
+	return nums[1:]
  1. Never use a count prefix:
 def parse_input(stream) -> list:
 	data = stream.read().strip().split()
 	if not data:
 		return []
 	try:
 		nums = [int(tok) for tok in data]
 	except ValueError:
 		raise
-
-	# If first token is count and matches remaining length, skip it
-	if len(nums) >= 2 and nums[0] == len(nums) - 1:
-		return nums[1:]
 	return nums

Update the docstring accordingly.

Committable suggestion skipped: line range outside the PR's diff.

🤖 Prompt for AI Agents 
In Python/uniqueNo.py around lines 43 to 44, the heuristic checking if nums[0]
== len(nums) - 1 is ambiguous and can drop a legitimate first element (e.g.,
when the unique number equals len(nums)-1); fix by removing the count-prefix
handling and always treat the input list as the full array (i.e., delete the
conditional that strips nums[0] and ensure all callers/parsing expect no leading
count), and update the module docstring to state that inputs must not include a
count prefix (or alternatively, if you prefer the opposite, mandate and parse a
required count prefix explicitly—pick one and make the code and docstring
consistent).

return nums
Comment on lines +43 to +45
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@sourcery-ai sourcery-ai bot Oct 27, 2025

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suggestion (code-quality): We've found these issues:

Suggested change
if len(nums) >= 2 and nums[0] == len(nums) - 1:
return nums[1:]
return nums
return nums[1:] if len(nums) >= 2 and nums[0] == len(nums) - 1 else nums



def main() -> int:
try:
arr = parse_input(sys.stdin)
except Exception:
print("Error: failed to parse input. Expected integers.")
return 1

if not arr:
demo = [2, 3, 5, 4, 5, 3, 4]
print("No input detected — running demo array:", demo)
print("Unique number:", unique_number(demo))
return 0

print(unique_number(arr))
return 0


if __name__ == '__main__':
raise SystemExit(main())