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

