蓝桥杯破损的楼梯

状态转移方程

dpi = dpi-1 + dpi-2

前提是dpi-1不是-1，dpi-2不是-1

代码

import java.util.Scanner;

public class Main{

   public static void main(String[] args) {
       Scanner s = new Scanner(System.in);
       long mod = (long)1e9+7;
       long[] dp = new long[100010];
       int N = s.nextInt();
       int M = s.nextInt();
       for(int i=0;i<M;i++)
           dp[s.nextInt()]=-1;
       dp[0]=1;
       for(int i=1;i<=N;i++){
           if(dp[i]==-1)
               continue;
           if(i>=1 && dp[i-1]!=-1)
               dp[i] = (dp[i]+dp[i-1])%mod;
           if(i>=2 && dp[i-2]!=-1)
               dp[i] = (dp[i]+dp[i-2])%mod;

       }
       if(dp[N]==-1)//这个测试点很无语
         System.out.println(0);
       else
         System.out.println(dp[N]);
       s.close();
   }
}