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

