//函数PreorderPrintLeaves应按照先序遍历的顺序输出给定二叉树BT的叶结点，格式为一个空格跟着一个字符。void PreorderPrintLeaves(BinTree BT){    if (BT == NULL)        return;    if (BT->Left == NULL && BT->Right == NULL)        printf(" %c", BT->Data);    PreorderPrintLeaves(BT->Left);    PreorderPrintLeaves(BT->Right);}