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

