△【LeetCode】Binary Tree Preorder Traversal

Given a binary tree, return the preorder traversal of its nodes' values.

For example:

Given binary tree 

{1,#,2,3}

,

1
\
2
/
3

return 

[1,2,3]

.

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<int> preorderTraversal(TreeNode *root)
{
vector<int> values;
stack<TreeNode*> stk;
TreeNode *p = root;
while(p!=NULL || !stk.empty())
{
while(p)
{
values.push_back(p->val);
stk.push(p);
p = p->left;
}

if(!stk.empty())
{
p = stk.top();
stk.pop();
p = p->right;
}

}
return values;
}
};

void preOrder1(BinTree *root)     //递归前序遍历
{
if(root!=NULL)
{
cout<<root->data<<" ";
preOrder1(root->lchild);
preOrder1(root->rchild);
}
}