题解 | 牛牛学数列6

#include <stdio.h>

int main() {
int arry[1000] = {0,1,1};
int n, sum;
scanf("%d",&n);
if(n == 1)
{
    printf("0");
}
if(n == 2 || n == 3)
{
    printf("1");
}
if(n>=4)
{
for(int i = 3;i<n;i ++ )
{
arry[i] = arry[i-3] + 2*arry[i -2] + arry[i - 1];
}
printf("%d",arry[n-1]);
}
    return 0;
}