---
title: "ByteByteGo: Lonely Integer"
url: https://perrotta.dev/2025/11/bytebytego-lonely-integer/
last_updated: 2026-01-03
---


[ByteByteGo: Lonely Integer](https://bytebytego.com/exercises/coding-patterns/bit-manipulation/lonely-integer):

```python
from typing import List
from functools import reduce

def lonely_integer(nums: List[int]) -> int:
    return reduce(lambda x, y: x ^ y, nums)
```

If you forget how to call `reduce`:

```python
from typing import List
from functools import reduce

def lonely_integer(nums: List[int]) -> int:
    ans = 0
    for num in nums:
        ans ^= num
    return ans
```