Leetcode 787. Cheapest Flights Within K Stops

Find the minimum-cost route from src to dst in a directed weighted graph with the constraint of at most k stops (i.e., a bound on the path length), returning -1 if no such route exists. This is a shortest-path problem with a path-length constraint, often handled by level-limited BFS/Dijkstra or K+1 iterations of Bellman–Ford.