odd_occurrences_in_array.py

"""
Task: OddOccurrencesInArray
Goal: Find value that occurs in odd number of elements.
Website: https://app.codility.com/programmers/lessons/2-arrays/odd_occurrences_in_array/
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A non-empty zero-indexed array A consisting of N integers is given. 
The array contains an odd number of elements, and each element of the 
array can be paired with another element that has the same value, except 
for one element that is left unpaired.

For example, in array A such that:

  A[0] = 9  A[1] = 3  A[2] = 9
  A[3] = 3  A[4] = 9  A[5] = 7
  A[6] = 9
the elements at indexes 0 and 2 have value 9,
the elements at indexes 1 and 3 have value 3,
the elements at indexes 4 and 6 have value 9,
the element at index 5 has value 7 and is unpaired.
Write a function:

def solution(A)

that, given an array A consisting of N integers fulfilling the above 
conditions, returns the value of the unpaired element.

For example, given array A such that:

  A[0] = 9  A[1] = 3  A[2] = 9
  A[3] = 3  A[4] = 9  A[5] = 7
  A[6] = 9
the function should return 7, as explained in the example above.

Assume that:

N is an odd integer within the range [1..1,000,000];
each element of array A is an integer within the range [1..1,000,000,000];
all but one of the values in A occur an even number of times.
Complexity:

expected worst-case time complexity is O(N);
expected worst-case space complexity is O(1), beyond input storage 
(not counting the storage required for input arguments).
"""

def solution(A):

    length = len(A)
    
    if length == 1:
        return A[0]
    
    else:
        myset = set(A) # Create a set of unique numbers in A
        for element in myset:
            count = A.count(element) # Count each and see if they occur an even or odd amount of times
            if count % 2 == 1:
                return element