vector<int> Solution::solve(TreeNode* A) {
vector<int> ans;
if(!A) return ans;
queue<TreeNode*> q;
q.push(A);
while(!q.empty()){
TreeNode* curr = q.front(); q.pop();
ans.push_back(curr->val);
if(curr->right)
{
q.push(curr->right);
}
if(curr->left)
{
q.push(curr->left);
}
}
reverse(ans.begin(),ans.end());
return ans;
}