Checking every column for duplicate characters
for ( int k = 0 ; k < m ; k ++ ) { if ( a [ i ] . charAt ( j ) == a [ i ] . charAt ( k ) && j != k ) { isPresent [ i ] [ j ] = true ; isPresent [ i ] [ k ] = true ; } } } } for ( int i = 0 ; i < n ; i ++ ) for ( int j = 0 ; j < m ; j ++ )