非递归实现前序中序和后序二叉树遍历 + 二叉树的层数遍历

typedef char ElemType;
typedef struct BiTNode {
    ElemType data;
    BiTNode *lchild, *rchild;
} BiTNode, *BiTree;

//前序遍历非递归算法
void PreOrderNotRecursion(BiTree T){
    stack S;
    BiTree p = T;
    while (p || !S.empty()) {
        while (p){
            cout<data<<" ";
            S.push(p);
            p = p->lchild;
        }
        p = S.top();
        S.pop();
        p = p->rchild;
    }
}
// 前序遍历非递归用vector
vector preorderTraversalUsevector(BiTree root){
        vector vec;
        if(!root){
            return vec;
        }
        vector nodes;
        nodes.push_back(root);
        while (!nodes.empty()){
            BiTree p = nodes.back();
            vec.push_back(p->data);
            nodes.pop_back();
            if(p->rchild)
                nodes.push_back(p->rchild);
            if(p->lchild)
                nodes.push_back(p->lchild);
        }
        return vec;
    }

//中序遍历非递归实现
void InOrderNotRecursion(BiTree T) {
    stack S;
    BiTree p = T;
    while (p || !S.empty()) {
        if (p) {  //遍历左子树
            S.push(p);   //每遇到非空二叉树先向左走
            p = p->lchild;
        }
        else {
            p = S.top();
            S.pop();
            cout << p->data << " ";
            p = p->rchild;
        }
    }
}

/*
 * 后序遍历非递归算法实现
 */
void PostOrderNotRecursion(BiTree T) {
    stack S;
    BiTree p = T;
    BiTree r = NULL; //用来记录最近访问的结点
    while (p || !S.empty()) {
        if (p) {
            S.push(p);
            p = p->lchild;
        } else {
            p = S.top();
            if (p->rchild && p->rchild != r) { //如果右子树存在且未被访问过
                p = p->rchild; //转向右
                S.push(p);//再压入栈
                p = p->lchild;//再走到最左
            } else {
                p = S.top();
                S.pop();
                cout << p->data << " ";
                r = p; //记录最近访问过的结点
                p = NULL; //结点访问完重置p指针，从而继续访问栈顶
            }//else
        }
    }//while
}

//层次遍历
void LevelOrder(BiTree T) {
    BiTree p;
    queue Q;
    Q.push(T);
    while (!Q.empty()) {
        p = Q.front();
        Q.pop();
        cout << p->data << " ";
        if (p->lchild != NULL) {
            Q.push(p->lchild);
        }
        if (p->rchild != NULL) {
            Q.push(p->rchild);
        }
    }
}