cost matrix
[400, 150, 400]
[400, 450, 600]
[300, 225, 300]
(0, 1) -> 150
(1, 0) -> 400
(2, 2) -> 300
lowest cost=850
cost matrix
[400, 150, 400,   1]
[400, 450, 600,   2]
[300, 225, 300,   3]
(0, 1) -> 150
(1, 3) -> 2
(2, 2) -> 300
lowest cost=452
cost matrix
[10, 10,  8]
[ 9,  8,  1]
[ 9,  7,  4]
(0, 0) -> 10
(1, 2) -> 1
(2, 1) -> 7
lowest cost=18
cost matrix
[10, 10,  8, 11]
[ 9,  8,  1,  1]
[ 9,  7,  4, 10]
(0, 1) -> 10
(1, 3) -> 1
(2, 2) -> 4
lowest cost=15
cost matrix
[ 4,  5,  6,  D]
[ 1,  9, 12, 11]
[ D,  5,  4,  D]
[12, 12, 12, 10]
(0, 1) -> 5
(1, 0) -> 1
(2, 2) -> 4
(3, 3) -> 10
lowest cost=20
cost matrix
[1, D, D, D]
[D, 2, D, D]
[D, D, 3, D]
[D, D, D, 4]
(0, 0) -> 1
(1, 1) -> 2
(2, 2) -> 3
(3, 3) -> 4
lowest cost=10
