duplicate_numbers_XOR.py

# You are given an array nums, where each number in the array appears either once or twice.

# Return the bitwise XOR of all the numbers that appear twice in the array, or 0 if no 
# number appears twice.

# Example 1:
# Input: nums = [1,2,1,3]
# Output: 1

# Explanation:
# The only number that appears twice in nums is 1.

# Example 2:
# Input: nums = [1,2,3]
# Output: 0

# Explanation:
# No number appears twice in nums.

# Example 3:
# Input: nums = [1,2,2,1]
# Output: 3

# Explanation:
# Numbers 1 and 2 appeared twice. 1 XOR 2 == 3.

 

# Constraints:

# 1 <= nums.length <= 50
# 1 <= nums[i] <= 50
# Each number in nums appears either once or twice.


class Solution:
    def duplicateNumbersXOR(self, nums: list[int]) -> int:
        
        res = 0
        mpp = {}

        for n in nums:
            if n in mpp:
                res = res^n
            mpp[n] = 1
        return res