flow.size: 6
row.1: 2,0,0,0,0,0
row.2: 0,3,0,0,8,3
row.3: 0,8,0,4,0,0
row.4: 2,0,0,6,1,0
row.5: 4,6,1,0,0,0
row.6: 0,0,0,0,0,0

