二叉树非递归遍历

1.先序非递归

vector<int> preorderTraversal(TreeNode* root) {
        if (root == nullptr) return{};
	 deque<TreeNode*> mq;
	 mq.push_front(root);

	 vector<int> nResult;
	 TreeNode *temp = nullptr;
	 while (mq.size() > 0)
	 {
		 temp = mq.front();
		 mq.pop_front();
		 nResult.push_back(temp->val);
		 if (temp->right)
			 mq.push_front(temp->right);
		 if (temp->left)
			 mq.push_front(temp->left);
	 }
	 return nResult;
    }

2.中序非递归

		stack<TreeNode*> mstack;
        TreeNode *temp = root;
        while(mstack.size() || temp)
        {
            while(temp){
                mstack.push(temp);
                temp = temp->left;
            }
            temp = mstack.top();
            nResult.push_back(temp->val);
            mstack.pop();
            temp = temp->right;
        }

3.后序非递归

vector<int> postorderTraversal(TreeNode* root) {
        if (root == nullptr) return{};
	 stack<int> ss;
	 deque<TreeNode *> list;
	 list.push_front(root);

	 TreeNode * temp = nullptr;
	 while (list.size() > 0)
	 {
		 temp = list.front();
		 list.pop_front();
		 ss.push(temp->val);

		 if (temp->left)
			 list.push_front(temp->left);
		 if (temp->right)
			 list.push_front(temp->right);
		 
	 }
	 vector<int> nResult;
	 while (ss.size() > 0)
	 {
		 nResult.push_back(ss.top());
		 ss.pop();
	 }
	 return nResult;
    }