二叉树的前序遍历
给出一棵二叉树，返回其节点值的前序遍历。
您在真实的面试中是否遇到过这个题？
Yes
样例
给出一棵二叉树 {1,#,2,3},
1
\
2
/
3
返回 [1,2,3].
/**
* Definition of TreeNode:
* class TreeNode {
* public:
* int val;
* TreeNode *left, *right;
* TreeNode(int val) {
* this->val = val;
* this->left = this->right = NULL;
* }
* }
*/ class Solution {
public:
/*
* @param root: A Tree
* @return: Preorder in ArrayList which contains node values.
*/
vector<int> l;
vector<int> preorderTraversal(TreeNode * root) {
// write your code here
if(root==NULL)
return l;
l.push_back(root->val);
preorderTraversal(root->left);
preorderTraversal(root->right);
return l;
}
};