Is Single Number easy or hard?

Single Number is categorized as an Easy problem on LeetCode. The hash map solution is simple to implement, while the XOR solution introduces a useful bit manipulation trick that appears in many technical interviews.

Single Number Python/Java solution

In Python or Java, the typical solution iterates through the array and XORs each element with a running variable. For example, start with result = 0 and update result ^= num for every value. After the loop finishes, result contains the single non-duplicated number.

How to solve Single Number in O(n)?

Iterate through the array and apply XOR with an accumulator variable. Because XOR cancels duplicate numbers, every pair disappears during the process. After processing all elements, the accumulator holds the element that appears once. The algorithm requires one pass and constant memory.

What is the best approach for Single Number?

The XOR bit manipulation approach is the best solution. By XORing all numbers in the array, duplicate values cancel each other out because a ^ a = 0. The remaining value is the unique number. This method runs in O(n) time and uses O(1) extra space.

Is Single Number asked at Google/Amazon/Meta?

Single Number is a common interview-style question used by companies like Amazon, Google, and Meta to evaluate understanding of bit manipulation and algorithmic reasoning. Variations of the problem often appear in coding screens and technical interviews.

What data structure is used in Single Number?

Two common techniques are used: a hash map for frequency counting and bit manipulation using XOR. The hash map approach stores counts for each number, while the XOR approach avoids extra data structures and relies on bitwise properties.

What is the time complexity of Single Number?

The optimal solution runs in O(n) time because the algorithm scans the array once and performs a constant-time XOR operation for each element. Space complexity is O(1) since only a single variable is used to track the result.