Given tree
TreeNode * root = new TreeNode ( 20 ) ; TreeNode * left = new TreeNode ( 12 ) ; TreeNode * right = new TreeNode ( 18 ) ; root -> children . push_back ( left ) ; root -> children . push_back ( right ) ; left -> children . push_back ( new TreeNode ( 11 ) ) ; left -> children . push_back ( new TreeNode ( 3 ) ) ; right -> children . push_back ( new TreeNode ( 15 ) ) ; right -> children . push_back ( new TreeNode ( 8 ) ) ;