first of all the initial distances as per the routing table are
A is connected to C and D
B is connected to C and D
C is connected to A and B
D is connected to A and B
distance between A-C is 1
distance between A-D is 2
distance between C-B is 3
distance between B-D is 2
at 1st exchange
routing table of A is [0,4,1,2]
routing table of B is [4,0,3,2]
routing table of C is [1,3,0,3]
routing table of D is [2,2,3,0]