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

