Flight Routes Check - Approach

Run Kosaraju or Tarjan to find all SCCs. Count how many distinct SCCs exist. If there is exactly one SCC containing all $n$ nodes, print "YES" (the graph is strongly connected). If there are two or more SCCs, print "NO" followed by two cities $a$ and $b$ in different SCCs.

It does not matter which pair you choose as long as they are in different components. Either $a$ cannot reach $b$ or $b$ cannot reach $a$ (or both).