题解 | 数楼梯

#include <stdio.h>

int main(void) {
    int n;
    scanf("%d", &n);

    if(n == 1){
        printf("1\n");
        return 0;
    }
    if(n == 2){
        printf("2\n");
        return 0;
    }
    long long a[100005];
    a[0] = 1, a[1] = 2;
    for(int i = 2; i <= n; i++){
        a[i] = a[i-1] + a[i-2];
        a[i] %= 998244353;
    }
    printf("%lld", a[n-1]);
    
    return 0;
}