no of ways to choose two square from 8*8 chessboard so that two square have a common side.
64c2-->choosing every possible pairs
now I know that i have to subtract all the invalid pairs .
just visualize,
picking either one of 4 cornered square =13+48=61 invalid squares that "that cornered " square should not pair with as they don't have a common side .
picking either one of all the similar type of square present like in row1 column 2 (visualise) =60 invalid squares that "that type" square should not pair with.
picking either one of all the similar type of square present like in row2 column 2 =59 invalid squares that "that type" squares should not pair with.
Then what?
Did you understand my approach ?
64c2-->choosing every possible pairs
now I know that i have to subtract all the invalid pairs .
just visualize,
picking either one of 4 cornered square =13+48=61 invalid squares that "that cornered " square should not pair with as they don't have a common side .
picking either one of all the similar type of square present like in row1 column 2 (visualise) =60 invalid squares that "that type" square should not pair with.
picking either one of all the similar type of square present like in row2 column 2 =59 invalid squares that "that type" squares should not pair with.
Then what?
Did you understand my approach ?