void flattenInternal(TreeNode* root, vector<TreeNode*> &v) {
if (root == null) return;
v.push_back(root);
if (root->left) {
flatten2(root->left, v);
}
if (root->right) {
flatten2(root->right, v);
}
}
TreeNode *flatten2(TreeNode *root) {
if(!root || (root->left == NULL && root->right == NULL)) return root;
if(root->left == NULL) return flatten2(root->right);
if(root->right == NULL) {
root->right = root->left;
root->left = NULL;
return flatten2(root->right);
}
TreeNode *stleft = flatten2(root->left);
TreeNode *stright = flatten2(root->right);
stleft->right = root->right;
root->right = root->left;
root->left = NULL;
return stright;
}
void flatten(TreeNode *root) {
flatten2(root);
}
