LeetCode 787 Cheapest Flights Within K Stops - Layer-by-Layer Relaxation

Standard Bellman-Ford runs $n-1$ iterations to find shortest paths with at most $n-1$ edges. Here, you run $k+1$ iterations because at most $k$ stops means at most $k+1$ flights. Use two distance arrays: $dist$ (current layer) and prev (previous layer). In each iteration, relax edges using prev and write results to $dist$.

Copy $dist$ to prev at the start of each iteration. This prevents using the same layer's updates within one iteration, which would allow longer paths than intended. Each iteration extends paths by exactly one edge.