Function hungarian_algorithm 

pub fn hungarian_algorithm(
    cost: &Array2<f64>,
) -> AssignmentResult<(Vec<usize>, f64)>

Solve the minimum-cost assignment problem using the Hungarian algorithm.

Given an n × m cost matrix, finds an assignment of n workers to jobs (one each) that minimises total cost. For non-square matrices the smaller dimension is padded with zeros.

Returns (assignment, total_cost) where assignment[i] = j means row i is assigned to column j.

Time complexity: O(n³) in the square case.

Errors

Returns an error if the cost matrix is empty.