##### 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

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