The Decision Tree

Before coding, ask yourself four questions:

$1.$ Are all edges weight $1$? Use BFS.

$2.$ Are weights non-negative? Use Dijkstra.

$3.$ Are there negative weights? Use Bellman-Ford.

$4.$ Do you need all-pairs distances and $N \leq 400$? Use Floyd-Warshall.

Each question narrows your options. Answer them in order. The first matching condition determines your algorithm choice. If none match cleanly, combine techniques or look for problem-specific structure to exploit.