题目

给出一棵二叉树，返回其节点值的前序遍历。

和中序遍历基本相同

C++代码

vector
     
       preorderTraversal(TreeNode *root) {	// write your code here	vector
      
        vec;	stack
       
         s;	TreeNode* p = root;	while (p || !s.empty())	{		while (p)		{			vec.push_back(p->val);			s.push(p);			p = p->left;		}		p = s.top();		s.pop();		p = p->right;	}	return vec;}