Java 代码

import java.util.Scanner;
public class Main{
    public static void main(String[]args)
    {
        Scanner in = new Scanner(System.in);
        int n,last = 0,ans = 0;
        while(true)
        {
            n = in.nextInt();
            if(n==2) {last +=2;ans += last;} //上一个是中心
            else if(n==1) {ans+=1;last = 0;} //不是中心，重置.
            else break;
        }
        System.out.println(ans);
    }
}