problem

solution

codes

#include
    
     int n, a[(int)1e5+10];int readint(){    int op=1,x=0; char ch=getchar();    while(ch<'0'||ch>'9'){
   if(ch=='-')op=-1; ch=getchar();}    while(ch>='0'&&ch<='9'){x=x*10+ch-'0'; ch=getchar();}    return op*x;}bool check(int dir){    int cnt = 0;    for(int i = 2; i <= n; i++, dir=!dir){ //到下一个数判断，方向需要改变        if(a[i]==a[i-1])continue;  //值相同毫无存在感        if((a[i]
     
      = 2)return false;        else i++,dir=!dir; //如果还没有炸，那么要跳过这个值再比较    }    return true;}int main(){    while(scanf("%d",&n)==1){        for(int i = 1; i <= n; i++)a[i]=readint();        printf("%s\n",n<=3||check(0)||check(1)?"Yes":"No");    }    return 0;}