/* No recusive to realize the travle of tree */void NoPreOrder( BiTree root ){/*{{{*/        Stack S;    BiTree P;    P = root;    S = CreateStack();    while( P!=NULL || !IsEmpty(S) )//判断条件分别对应着                                   //1,S is not empty && P = NULL 当前节点为上一节点的右子树,右子树为空,但还有上一节点的上一节点的右子树                                   //未被遍历                                   //2.s is empty && p != NULLQ.情况唯一 :初始根节点被退出,但还有右子树需要遍历                                   //3,s is not empty $$ p != NULL 栈未被退完,而且当前右子树也不为空    {        while( P != NULL )        {            visit( P );//先序访问根节点            Push( P , S );//根节点入栈,以备访问右子树            P = P->Left;//继续访问左子树        }        if( !IsEmpty(S) )        {             P = Pop( S );//出栈            P = P->Right;//遍历被访问过的根节点的右子树        }    }}/*}}}*/