// per generare in fila tutte le pemutazioni
      public bool NextPermutation(int[] numList)
      {
         /*
         Knuths
         1. Find the largest index j such that a[j] < a[j + 1]. If no such index exists, the permutation is the last permutation.
         2. Find the largest index l such that a[j] < a[l]. Since j + 1 is such an index, l is well defined and satisfies j < l.
         3. Swap a[j] with a[l].
         4. Reverse the sequence from a[j + 1] up to and including the final element a[n].
         */
         var largestIndex = -1;
         for (var i = numList.Length - 2; i >= 0; i--)
         {
            if (numList[i] < numList[i + 1]) {
               largestIndex = i;
               break;
            }
         }

         if (largestIndex < 0) return false;

         var largestIndex2 = -1;
         for (var i = numList.Length - 1 ; i >= 0; i--) {
            if (numList[largestIndex] < numList[i]) {
               largestIndex2 = i;
               break;
            }
         }

         var tmp = numList[largestIndex];
         numList[largestIndex] = numList[largestIndex2];
         numList[largestIndex2] = tmp;

         for (int i = largestIndex + 1, j = numList.Length - 1; i < j; i++, j--) {
            tmp = numList[i];
            numList[i] = numList[j];
            numList[j] = tmp;
         }

         return true;
      }