public SudokuNodePile(SudokuNodePileNode node)
 {
     this.head = node;
     this.tail = node;
 }
 public SudokuNodePile(SudokuNode node)
 {
     SudokuNodePileNode n = new SudokuNodePileNode(node);
     this.head = n;
     this.tail = n;
 }