Topological Sort (Algorithm)

$\text{TOPOLOGICAL\_SORT}(G)$:

1. While vertices remain unsorted:
   1. Select any unsorted vertex and add to a stack
   2. While stack is not empty:
      1. Inspect top element $u$ on stack
      2. If $u$ has no unsorted neighbours:
         1. Pop $u$ from stack and add to list $L$
      3. Else: add unsorted neighbours of $u$ to stack
2. Return sorted list $L$