dp [ i ] [ j ] indicates the length of LCS of A of length i & B of length j
vector < vector < int > > dp ( n + 1 , vector < int > ( m + 1 , 0 ) ) ; for ( int i = 0 ; i < n + 1 ; i ++ ) { for ( int j = 0 ; j < m + 1 ; j ++ ) {