Backtracking: enumerate valid subsets without reusing indexes

Backtracking: Count subsets of input indexes whose positive values sum to target. Each index may be used at most once; equal values at different indexes remain distinct choices.

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

Output: A JSON integer subset count.

Constraints:

0 <= nums.length <= 24
Every nums value is a positive integer
target is a non-negative integer

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

Difficulty: HARD. Variant: 12. Favor a pragmatic solution that is easy to ship, read, and adapt.

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

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.