一块40克的砝码，摔成4块，利用天平，刚好可以称出1~40g所有整数克，问：这4块分别是多少克

    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();//记录每组数的值 每组数a<=b<=c<=d
        List<Integer> rlist = new ArrayList<>();//记录最后的结果
        
        for(int i = 1; i <= 10 ; i++) {
            for(int j = i; j <= 13 ; j++) {
                for(int k = j; k <= 19 ; k++) {
                    list.add(i);
                    list.add(j);
                    list.add(k);
                    list.add(40-i-j-k);
                }
            }    
        }
        
        int a,b,c,d;
        int len = list.size()/4;
        for (int i = 0; i < len; i++) {
            a = list.get(4*i);
            b = list.get(4*i+1);
            c = list.get(4*i+2);
            d = list.get(4*i+3);
            if(result(a, b, c, d)) {
                rlist.add(a);
                rlist.add(b);
                rlist.add(c);
                rlist.add(d);
            }
        }
        len = rlist.size()/4;
        for(int i = 0; i < len; i++) {
            System.out.println("40 = "+rlist.get(4*i)+" + "+rlist.get(4*i+1)+" + "+rlist.get(4*i+2)+" + "+rlist.get(4*i+3));
        }
    }
    
    public static boolean result(int a,int b,int c,int d){
        TreeSet<Integer> set = new TreeSet<>();
        int[] arr = {-1,0,1};
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr.length; j++) {
                for (int k = 0; k < arr.length; k++) {
                    for (int l = 0; l < arr.length; l++) {
                        int sum = a*arr[i]+b*arr[j]+c*arr[k]+d*arr[l];
                        
                        if(sum > 0) set.add(sum);
                    }
                }
            }
        }
        if(set.size() == 40)
            return true;
        else
            return false;
    }