145. Binary Tree Postorder Traversal

class Solution {
public:
vector<int> postorderTraversal(TreeNode* root) {
vector<int>res;
postorder(root,res);
return res;
}
void postorder(TreeNode* root,vector<int>&res){
if(root==NULL)return ;
if(root->left!=NULL)postorder(root->left,res);
if(root->right!=NULL)postorder(root->right,res);
res.push_back(root->val);
}
};

// iterator
// reference:http://zhidao.baidu.com/link?url=hi29Y_FNWekIU9L4YJV0hqzuzB6YXtQdH-7BJvfUUvzB731gxdH1_zMKfAZkBUo4JlhupBobBuq_usGqy-nrm_J9Fc79KE6i0WJ7tvb6sk3
class Solution {
public:
vector<int> postorderTraversal(TreeNode* root) {
vector<int>res;
if(root==NULL)return res;
stack<TreeNode*>s;
TreeNode*p=root;
while(p){
s.push(p);
p=p->left;
while(!s.empty()){
p=s.top();
//cout<<p->val<<endl;
if(p->right){
//cout<<p->right->val<<endl;
s.push(p->right);
TreeNode*q=p->right;
p->right=NULL;
p=q;
while(p->left){
}else{
s.pop();
res.push_back(p->val);
}
return res;
}

};

// another iterator
class Solution {
public:
vector<int> postorderTraversal(TreeNode* root) {
vector<int>res;
if(root==NULL)return res;
stack<TreeNode*>s;
s.push(root);
while(!s.empty()){
TreeNode*p=s.top();
s.pop();
res.push_back(p->val);
if(p->left)s.push(p->left);
if(p->right)s.push(p->right);
}
std::reverse(res.begin(),res.end());
return res;
}

};