public class sumCnt {
    public static void main(String[] args){
        int[] a = {1, 2, 4, 3, 5};
        System.out.println(f(a.length - 1, 4, a));
    }
    // n: 遍历数组a下标,从0到a.length-1;
    public static int f(int n, int m, int[] a){
        if(n == 0){
            return a[n] == m ? 1: 0;
        }
        if(a[n] == m){
            return f(n-1, m, a) + 1;
        }else if(a[n] < m){
            return f(n-1, m, a) + f(n-1, m - a[n], a);
        }else{
            return f(n-1, m, a);
        }
    }
}

仅供参考哈！