其它
$A$ and $B$ play a game as follows. First $A$ says $1, 2$ or $3$. Then $B$ can add $1, 2$ or $3$ to the number the first player said. The game continues with the players playing alternately, in each turn adding $1, 2$ or $3$ to the previous number. For example, A can say $2$, then B can say $5$, then A could say $6$, and so on. The player who says $100$ wins. Who has the winning strategy? 
Overseas Competition->Knowledge Point->Combinatorics->Strategies and Operations
Observe that B can always say a multiple of 4 in his turn. For example, consider the following sequence of moves: A-1; B-4; A-6; B-8 and so on. Regardless of what A says, B can always say a multiple of 4. Hence B will say 100 and will win 