flow.size: 8
row.1: 7,0,0,7,4,0,0,0
row.2: 0,0,6,9,5,0,5,0
row.3: 0,0,3,0,0,0,0,0
row.4: 0,0,2,0,1,8,0,0
row.5: 0,0,0,0,9,0,0,0
row.6: 0,0,0,6,0,0,0,0
row.7: 0,3,0,2,0,0,1,4
row.8: 0,0,0,0,0,0,0,8

