3.
/**
* 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> inorderTraversal(TreeNode* root) {
stack<TreeNode*>stk;
vector<int> res;
auto p=root;
while(p || stk.size())
{
while(p)
{
stk.push(p);
p=p->left;
}
p=stk.top();
stk.pop();
res.push_back(p->val);
p=p->right;
}
return res;
}
};
