非递归实现二叉树的后序遍历、前序遍历、中序遍历

vector<int> postOrder(TreeNode *root)//后序遍历
{
vector<int> res;
if (root == NULL) return res;

TreeNode *p = root;
stack<TreeNode *> sta;
TreeNode *last = root;
sta.push(p);
while (!sta.empty())
{
p = sta.top();
if ((p->left == NULL && p->right == NULL) || (p->right == NULL && last == p->left) || (last == p->right))
{
res.push_back(p->val);
last = p;
sta.pop();
}
else
{
if (p->right)
sta.push(p->right);
if (p->left)
sta.push(p->left);
}

}

return res;
}

void preOrder_stack(Node root) {//先序遍历

Stack<Node> stack = new Stack<Node>();
Node node = root;

while (node|| !stack.empty()){//左孩子压栈
while (node) {//压栈之前先访问
printNode(node);
stack.push(node);
node = node.getLeftNode();

}
if(!stack.empty())
{
node = stack.pop();
node = node.getRightNode();
}
}
}

void inOrder_Stack(Node root) {//中序遍历

Stack<Node> stack = new Stack<Node>();
Node node = root;

while (node || !stack.empty()) {
while (node) {
stack.push(node);//直接压栈
node = node.getLeftNode();
}
if (!stack.empty()) {
node = stack.pop();//出栈并访问
printNode(node);
node = node.getRightNode();
}
}
}