题解 | 牛牛学数列6

#include <stdio.h>

int main() {
    int n = 0;
    int count = 0;
    int arr[21];
    arr[0] = 0;
    arr[1] = 1;
    arr[2] = 1;
    scanf("%d", &n);
    for (int i = 4; i <= n; i++) {
        arr[i - 1] = arr[i - 4] + arr[i - 3] * 2 + arr[i - 2];
       
    }
    if (n == 1) {
        printf("0");
    } else if (n == 2 || n == 3) {
        printf("1");
    } else {
 printf("%d", arr[n - 1]);
    }
    return 0;
}