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先序遍历，用递归来做，简单的不能再简单了。代码如下：
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
private:
vector<int> res;
public:
void getOrder(TreeNode* node)
{
if(node==NULL)
return ;
else
{
res.push_back(node->val);
getOrder(node->left);
getOrder(node->right);
}
return ;
}
vector<int> preorderTraversal(TreeNode* root) {
if(root==NULL)
return res;
res.push_back(root->val);
getOrder(root->left);
getOrder(root->right);
return res;
}
};
但是题目要求用迭代来做。
迭代的代码如下：
/**
* Definition for a binary tree node.
* 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> res;
stack<TreeNode*> stk;
while(root!=NULL||!stk.empty())
{
if(root!=NULL)
{
res.push_back(root->val);
stk.push(root);
root=root->left;
}
else
{
root=stk.top()->right;
stk.pop();
}
}
return res;
}
};
Binary Tree Preorder Traversal
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原文地址：http://www.cnblogs.com/qiaozhoulin/p/4746221.html
