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 && set.first() == 1)
             return true;
         else
             return false;
     }