class Solution{

public:

void traversal(TreeNode* cur, vector <int>&vec){

if (cur==NULL) return;

vec.push_back(cur->val);

traversal(cur->left,vec);

traversal(cur->right,vec);

}

vector<int> preoderTraversal(TreeNode* root ){

vector<int> result;

traversal(root,result);

return result;

}

};