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

