二叉树那些非递归遍历

#include
#include
using namespace std;

class TreeNode{
public:
	TreeNode(char val):val(val),left(nullptr),right(nullptr){}
	char val;
	TreeNode* left,*right;
};

void preOrder(TreeNode* root){
	if(!root)return;
	stackst;
	st.push(root);
	while(!st.empty()){
		auto tmp=st.top();
		st.pop();
		cout<val<<",";
		auto l=tmp->left,r=tmp->right;
		if(r)st.push(r);
		if(l)st.push(l);
	}
}

void backOrder(TreeNode* root){
	if(!root)return;
	stackst;
	TreeNode* pre=nullptr,*p=root;
	while(p!=nullptr || !st.empty()){
		while(p && p!=pre){
			st.push(p);
			p=p->left;
		}
		if(st.empty())return;
		auto tmp=st.top();
		//st.pop();
		if(tmp->right && tmp->right!=pre){
			p=tmp->right;
			
		}else {
			cout<val<<",";
			pre=tmp;
			st.pop();
		}
	}
}

void midOrder(TreeNode* root){
	if(!root)return;
	stackst;
	auto p=root;
	while(p || !st.empty()){
		while(p){
			st.push(p);
			p=p->left;
		}
		auto tmp=st.top();
		st.pop();
		cout<val<<",";
		p=tmp->right;
	}
}

void pre(TreeNode* root){
	if(!root)return;
	cout<val<<",";
	pre(root->left);
	pre(root->right);
}

int main(){
	TreeNode A('A');
	TreeNode B('B');
	TreeNode C('C');
	TreeNode D('D');
	TreeNode E('E');
	TreeNode F('F');
	TreeNode G('G');
	F.right=&G;
	C.left=&E;C.right=&F;
	B.right=&D;
	A.left=&B;A.right=&C;
	
	TreeNode* p=&A;
	cout<<"pre:"<