MissingNumber

MissingNumber

A Zig solution for finding the missing number in sequential series.

Approach

Uses the arithmetic sum formula: the expected sum of a contiguous range [min, max] is (max + min) * (max - min + 1) / 2. Subtracting the actual sum of the provided numbers gives the missing value in O(n) time with O(1) extra space.

The solution is structured as a library (root.zig) with a thin CLI driver (main.zig), making the core logic reusable and independently testable.

Build & Run

# requires zig 0.14+
make run

Test

make test

53 tests across three modules (solver, parser, orchestration) covering happy paths, edge cases, error paths, negative numbers, large ranges, input format variations, overflow detection, duplicate detection, and input validation.

Design Considerations

• Library separation: Core logic is decoupled from I/O, enabling integration into larger systems or alternative frontends.
• Allocator-driven: All allocations go through Zig's allocator interface, giving callers full control over memory strategy.
• Extensibility: parseLine and findMissing are independent. The parser could be swapped for streaming input, and the algorithm could be extended to handle multiple missing values.