struct TreeNode {

int val;

TreeNode *left;

TreeNode *right;

};

#include<vector>

#include<stack>

using namespace std;

class Solution {

public:

vector<int> inorderTraversal(TreeNode* root) {

vector<int> ret;

if (!root) return ret;

bool goleft = true;

stack<TreeNode*> s;

s.push(root);

while (s.size() > 0) {

TreeNode* node = s.top();

if (goleft && node->left) {

s.push(node->left);

goleft = true;

} else {

ret.push_back(node->val);

s.pop();

if (node->right) {

s.push(node->right);

goleft = true;

} else {

goleft = false;

}

}

}

return ret;

}

};