题解 | 牛牛学数列6

#include <stdio.h>

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

    int shuzu[n];
    if (n >= 1) shuzu[0] = 0;
    if (n >= 2) shuzu[1] = 1;
    if (n >= 3) shuzu[2] = 1;
    if (n == 1){
        printf("%d", shuzu[0]);
    }
    if ((n == 2) || (n == 3)){
        printf("%d", shuzu[1]);
    }

    if (n >= 4){
        for (int i = 3; i < n; i++){
            shuzu[i] = shuzu[i - 3] + 2 * shuzu[i - 2] + shuzu[i - 1];
        }
    }

    printf("%d", shuzu[n - 1]);
    return 0;
}