Bit manipulation: use xor properties to isolate an unpaired value

Bit manipulation: Every value in nums appears exactly twice except one value that appears once. Return the single unpaired value.

Input: A JSON object { "nums": number[] }.

Output: A JSON integer containing the unpaired value.

Constraints:

1 <= nums.length <= 100001
nums.length is odd
Exactly one value appears once and every other value appears twice

Read one JSON value from stdin and print exactly one JSON-serialized answer to stdout with no extra text.

Difficulty: HARD. Variant: 21. Balance correctness, maintainability, and clear review-ready code.

Practice context

This coding (algo) exercise trains prompt interpretation, explicit assumptions, a concrete response, and a concise explanation of the decisions made. It is marked hard difficulty.

The signed-in workspace provides the tools required by the round, such as recording, code execution, diagrams, structured notes,

What this task practices

This coding (algo) exercise trains the same sequence expected in an interview: understand the prompt, make assumptions explicit, produce a concrete answer, and explain the decisions behind it. The task is marked hard difficulty. The private workspace adds the tools required by this round, such as recording, code execution, diagrams, evidence panels, or structured notes. It also preserves the attempt so later feedback can be compared with previous work. Evaluation is based on task-specific criteria and the candidate seniority selected in the preparation path. Public pages never expose the reference solution, hidden tests, evaluator instructions, or another candidate’s work.