Function pass_at_k 

pub fn pass_at_k(n: usize, c: usize, k: usize) -> f64

Compute pass@k: unbiased estimator of functional correctness.

Formula: 1 - C(n-c, k) / C(n, k)

where n = total samples, c = correct samples, k = top-k threshold.

Returns a value in [0, 1] where 1.0 means all k samples pass.

Arguments

• n - Total number of generated code samples
• c - Number of correct (passing) samples
• k - Number of samples to consider (typically 1, 10, or 100)

Edge Cases

• If k > n, returns if c > 0 { 1.0 } else { 0.0 }
• If c >= n, returns 1.0
• If c == 0, returns 0.0