1342 摆放小球

1342 摆放小球

⭐️考点：第二类斯特林数
🌟难度：中等
📖

📚

import java.util.Arrays;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class Main {
    static long MOD = 1000000007;

    static long[][] dp = new long[1010][1010];

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int k = sc.nextInt();
        for(long[] x : dp){
            Arrays.fill(x,-1);
        }
        System.out.println(stirling(n ,k));

    }

    static long stirling(int n,int k){
        if(k > n || k == 0) return 0;
        if(k == n || k == 1) return 1;

        if(dp[n][k] != -1){
            return dp[n][k];
        }

        dp[n][k] = (1l * k * stirling(n - 1,k) % MOD + stirling(n - 1,k - 1)) % MOD;
        return dp[n][k];
    }
}