class Solution {
public:
int numWays(int n) {
if(n<=1) return 1;
int dp[n+1];//多申请一个空间,输入2会越界
const int mod = 1e9+7;
dp[0] =1;
dp[1] = 1;
for(int i =2;i<n+1;i++){
dp[i] =(dp[i-1]+dp[i-2])%mod;
}
return dp[n];
}
};