백준1182_부분집합의 합

 

package backjoon;
 
import java.util.Scanner;
 
/**
 *  알고리즘 경우의 수 부분집합 게시글 참고!!
 */
 
public class b1182 {
 
    static int cnt = 0;
 
    public static void sum(int[] arr, int[] arr_index, int size, int N, int S, int index) {
        int sum = 0;
 
        for (int i = 0; i < size; i++) {
            int j = arr_index[i];
            sum += arr[j];
        }
        if (size != 0) {
            if (sum == S) {
                cnt++;
            }
        }
    }
 
    public static void subset(int[] arr, int[] arr_index, int size, int N, int S, int index) {
        // 인덱스로 사용할 부분집합만 만들어줌
        if (N == index) {
            sum(arr, arr_index, size, N, S, index);
            return;
        }
        arr_index[size] = index;
        subset(arr, arr_index, size + 1, N, S, index + 1);
        subset(arr, arr_index, size, N, S, index + 1);
    }
 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int S = sc.nextInt();
        int[] arr = new int[N];
        int[] arr_index = new int[N];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = sc.nextInt();
        }
 
        subset(arr, arr_index, 0, N, S, 0);
        System.out.println(cnt);
    }
}