Shortest Directed Cycle Through a Node

Round 4 of a 4-round NG loop. BFS from the target node in a directed graph; return the moment BFS re-enters the node. Requirements Directed graph; given a node v, return the length of the shortest cycle containing v. BFS from v over the directed edges; the first time v is rediscovered (as a target), the BFS depth is the answer. Handle no-cycle case (return -1 or infinity). Examples Edges [(0,1),(1,2),(2,0)], v = 0 → 3. Edges [(0,1),(1,2)], v = 0 → -1. Notes Strictly directed; do not relax to undirected. BFS layer 0 is v itself; the first re-discovery during expansion is the cycle length. Common bug: marking v as visited immediately blocks the re-entry. Preparation Write the directed BFS-from-source version from memory in under 12 min. Practice the "re-entry detection" pattern (don't mark v visited until after pop).