example graph  heap=0 8 9 5 7  array=0 8 9 5 7  BF=0 8 9 5 7  -> all agree

2000 random non-negative digraphs: 0 disagreements

        n      m    array(ms)   heap(ms)
     1000    8000        2.1        0.5
     1000  250000        7.2        4.5
     2000   16000        6.9        1.0
     2000 1000000       27.9       18.4
     4000   32000       25.9        2.1
     4000 4000000      113.7       83.8
