Topological Order (lexicographically smallest)
Given a directed graph (edge u v = u before v), print the lexicographically smallest topological order, or CYCLE if the graph has a cycle.
Input: line 1 V E; then E lines u v.
Output: the lex-smallest topo order (space-separated), or CYCLE.
Use Kahn's algorithm with a min-heap of in-degree-0 nodes. Fewer than V popped ⇒ cycle.