题目出处点这里
动态规划,就像找规律一样,注意从每种情况中进行分类即可
**
代码如下:(注意每次都要取模,不然无法AC)
package reintroduction_recursion;
import java.util.Scanner;
public class P1990 {
static int res;
static int[] f = new int[1000001];
static int[] g = new int[1000001];
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
f[0] = 1;g[0] = 1;
f[1] = 1;g[1] = 2;
f[2] = 2;g[2] = 4;
f[3] = 5;g[3] = 9;
//f(0) = 1
//f(1) = 1
//f(2) = 2
//f(3) = 1+2+2*(1) = 5
//f(4) = 2+5+2*(1+1) = 11
//f(5) = 5+11+2*(1+1+2) = 24
//f(n) = f(n-2)+f(n-1)+2*(f(0)+f(1)+……+f(n-3))
//设f(0)+f(1)+……+f(n)=g(n),所以有f(0)+f(1)+……+f(n-3)=g(n-3)
//因此f(n) = f(n-2)+f(n-1)+2*g(n-3)
for (int i = 4; i <= n; i++) {
f[i] = f[i-2]%10000+f[i-1]%10000+2*g[i-3]%10000;
g[i] = g[i-1]%10000+f[i]%10000;
}
System.out.println(f[n]%10000);
}
}