Problem Description
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.
Key Insights
- The XOR operation has a unique property: x XOR x = 0 and x XOR 0 = x. This means that if we XOR a number with itself, the result is 0.
- If a number appears twice in the array, it contributes to the XOR result, while numbers that appear only once do not affect the result.
- We can utilize a hash set or a dictionary to track the occurrence of each number in the array.
Space and Time Complexity
Time Complexity: O(n) - We traverse the array once to count occurrences and then again to compute the XOR. Space Complexity: O(n) - We may use additional space to store the count of each number.
Solution
To solve the problem, we can use a hash set to track the numbers that appear twice. We iterate through the array and update our hash set accordingly. In a second pass, we compute the XOR of all numbers that appeared twice. This approach is efficient because it allows us to determine the result in linear time.