public class Main {
 
    static int countSequences(int n, int[] b) {
        int[] dp = new int[n+2];
        //dp[i] = number of ways to reach index i
        dp[1] = 1; //one way to reach 1
        dp[2] = 1; //can jump 2 so directly reach a[2]
        for (int i = 3; i <= n; i++) {
            // you can come to i from i-1 only normally
            dp[i] = dp[i-1];
            if(b[i-2]==2) dp[i] += dp[i-2];
        }
        return dp[n];
    }
 
    public static void main(String[] args) {
        int n = 5;
        int[] b = {1, 2, 1, 1, 2}; // Example array b
 
        System.out.println(countSequences(n, b));
    }
}
 

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