##### Short Problem Definition:

Find value that occurs in odd number of elements.

##### Link

##### Complexity:

expected worst-case time complexity is `O(N)`

expected worst-case space complexity is `O(1)`

##### Execution:

This problem can be found in many algorithm books. A xor A cancels itself and B xor 0 is B. Therefore A xor A xor B xor C xor C is B.

##### Solution:

```
def solution(A):
missing_int = 0
for value in A:
missing_int ^= value
return missing_int
```