topological order: s b a c d e

process  d/pi s  d/pi a  d/pi b  d/pi c  d/pi d  d/pi e
      s     0/-     6/s     3/s   inf/-   inf/-   inf/-
      b     0/-     1/b     3/s     7/b    10/b   inf/-
      a     0/-     1/b     3/s     2/a     6/a   inf/-
      c     0/-     1/b     3/s     2/a    -1/c     4/c
      d     0/-     1/b     3/s     2/a    -1/c     0/d
      e     0/-     1/b     3/s     2/a    -1/c     0/d

shortest path to e: s b a c d e   weight 0
