题解 | #公约数#

import java.util.Scanner;

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

        while(in.hasNext()){
            solution(in);
        }
    }

    /**
     * 动态规划
     *
     * dp[j][x]表示选择j张牌且这些牌上数字的乘积与A的最大公约数为x的方案数
     *
     * dp[j+1][gcd(a/x, cards[i])*x] += dp[j][x]
     *
     * @param in
     */
    private static void solution(Scanner in){
        int n = in.nextInt();
        int k = in.nextInt();
        int a = in.nextInt();
        int b = in.nextInt();

        int[] cards = new int[n+1];
        for(int i=1; i<=n; i++){
            cards[i] = in.nextInt();
        }

        long[][] dp = new long[n+1][a+1];
        dp[1][gcd(cards[1], a)] = 1;
        for(int i=2; i<=n; i++){
            for(int j=i-1; j>0; j--){
                for(int x=a; x>0; x--){
                    if(dp[j][x] != 0){
                        dp[j+1][gcd(a/x, cards[i])*x] += dp[j][x];
                    }
                }
            }
            dp[1][gcd(cards[i], a)] += 1;
        }

        long result = 0;
        for(int i=b; i<=a; i++){
            result += dp[k][i];
        }

        System.out.println(result);
    }

    /**
     * 最大公约数
     * @param a
     * @param b
     * @return
     */
    private static int gcd(int a, int b){
        return b>0 ? gcd(b, a%b) : a;
    }
}