C ++ program to find no . of ways to fill a 3 xn board with 2 x1 dominoes .
#include <iostream> NEW_LINE using namespace std ; int countWays ( int n ) { int A [ n + 1 ] , B [ n + 1 ] ; A [ 0 ] = 1 , A [ 1 ] = 0 , B [ 0 ] = 0 , B [ 1 ] = 1 ; for ( int i = 2 ; i <= n ; i ++ ) { A [ i ] = A [ i - 2 ] + 2 * B [ i - 1 ] ; B [ i ] = A [ i - 1 ] + B [ i - 2 ] ; } return A [ n ] ; }