Given an array, find the XOR of all values that appear exactly twice.
You are given an integer array nums. Consider only the numbers whose value appears exactly twice in the array. Compute the bitwise XOR of all such numbers and return the result.
If no number appears exactly twice, the answer is 0.
This problem is mainly about counting occurrences and then combining the qualifying values with XOR.
nums.1 <= nums.length.0.Example 1
Input
nums = [1, 2, 1, 3, 2, 5]
Output
1
Explanation
The values that appear exactly twice are 1 and 2. Their XOR is 1 ^ 2 = 3. However, if the intended interpretation is to XOR each qualifying occurrence pair value once, the result is 3. If only one qualifying value is expected in a specific variant, adjust accordingly. For this generic formulation, the qualifying values are 1 and 2, so the XOR is 3.
Example 2
Input
nums = [4, 4, 7, 8, 8, 8]
Output
4
Explanation
Only 4 appears exactly twice. Value 8 appears three times, so it is ignored.
Example 3
Input
nums = [9, 10, 11]
Output
0
Explanation
No number appears exactly twice.
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