CodeForces-a

A. Chess For Three
time limit per test1 second
memory limit per test256 megabytes
inputstandard input
outputstandard output
Alex, Bob and Carl will soon participate in a team chess tournament. Since they are all in the same team, they have decided to practise really hard before the tournament. But it’s a bit difficult for them because chess is a game for two players, not three.

So they play with each other according to following rules:
Alex and Bob play the first game, and Carl is spectating;
When the game ends, the one who lost the game becomes the spectator in the next game, and the one who was spectating plays against the winner.
Alex, Bob and Carl play in such a way that there are no draws.
Today they have played n games, and for each of these games they remember who was the winner. They decided to make up a log of games describing who won each game. But now they doubt if the information in the log is correct, and they want to know if the situation described in the log they made up was possible (that is, no game is won by someone who is spectating if Alex, Bob and Carl play according to the rules). Help them to check it!
Input
The first line contains one integer n (1 ≤ n ≤ 100) — the number of games Alex, Bob and Carl played.
Then n lines follow, describing the game log. i-th line contains one integer ai (1 ≤ ai ≤ 3) which is equal to 1 if Alex won i-th game, to 2 if Bob won i-th game and 3 if Carl won i-th game.
Output
Print YES if the situation described in the log was possible. Otherwise print NO.
这道题的思路是找输家，这一盘的输家不能出现在下一盘。
核心代码是：

sj=3；
for(i=1;i<=3;i++)
{
    if(sj!=i&&i!=yj)
        sj=i;
}//sj为不能出现的数，也就是上一盘的输家，刚开始为3；yj为输入的数（这道题一个一个数比较），也就是这一盘的赢家；所以剩下的就是输家，在下一盘中不能出现。