题解 | #实现二叉树先序，中序和后序遍历#
实现二叉树先序，中序和后序遍历
http://www.nowcoder.com/practice/a9fec6c46a684ad5a3abd4e365a9d362
/**
* struct TreeNode {
* int val;
* struct TreeNode *left;
* struct TreeNode *right;
* };
*/
class Solution {
public:
/**
*
* @param root TreeNode类 the root of binary tree
* @return int整型vector<vector<>>
*/
vector<int> first;
vector<int> mid;
vector<int> last;
vector<vector<int> > threeOrders(TreeNode* root) {
// write code here
firstorder(root);
midorder(root);
lastorder(root);
vector<vector<int>> threeorders;
threeorders.push_back(first);
threeorders.push_back(mid);
threeorders.push_back(last);
return threeorders;
}
void firstorder(TreeNode *root){
if(root!=NULL){
first.push_back(root->val);
if(root->left!=NULL) firstorder(root->left);
if(root->right!=NULL) firstorder(root->right);
}
return;
}
void midorder(TreeNode *root){
if(root!=NULL){
if(root->left!=NULL) midorder(root->left);
mid.push_back(root->val);
if(root->right!=NULL) midorder(root->right);
}
return;
}
void lastorder(TreeNode *root){
if(root!=NULL){
if(root->left!=NULL) lastorder(root->left);
if(root->right!=NULL) lastorder(root->right);
last.push_back(root->val);
}
return;
}
};
采用递归的方法进行，意料之外的时间最快，内存却较大，有点疑惑，观看大部分题解都是采用同样的递归方法，为何会有此不同，望解惑！
