FindTheMissingElement.py

'''
Consider an array of non-negative integers.
A second array is formed by shuffling the elements of the first array and deleting a random element.
Given these two arrays, find which element is missing in the second array.

Here is an example input, the first array is shuffled and the number 5 is removed to construct the second array.

Input:

    finder([1,2,3,4,5,6,7], [3,7,2,1,4,6])

Output:

    5 is the missing number.
'''

# Method 1 (Not Optimal)
'''
def finder(arr1, arr2):

    arr1.sort()
    arr2.sort()

    for num1, num2 in zip(arr1, arr2):
        if num1 != num2:
            return num1
    return arr1[-1]

# Method 2

import collections

def finder(arr1, arr2):

    d = collections.defaultdict(int)

    for num in arr2:
        d[num] += 1

    for num in arr1:
        if not d[num]:
            return num
        else:
            d[num] -= 1
'''
# Method 3 (Using XOR)

def finder(arr1, arr2):
    result = 0

    # Perform an XOR between the numbers in the arrays
    for num in arr1 + arr2:
        result ^= num
        print(result)

    return result