贴一些第一题吧，迭代的思路 public TreeNode cyclicShiftTree (TreeNode root, int k) { // write code here List<TreeNode> up = new ArrayList<>(); up.add(root); while (!up.isEmpty()) { List<TreeNode> down = new ArrayList<>(); for (int i = 0; i < up.size(); i++) { TreeNode node = up.get(i); down.add(node.left); down.add(node.right); } int index = 0; for (int i = 0; i < up.size(); i++) { TreeNode node = up.get(i); node.left = down.get((index++ - k % down.size() + down.size()) % down.size()); node.right = down.get((index++ - k % down.size() + down.size()) % down.size()); } up.clear(); for (int i = 0; i < down.size(); i++) { if (down.get(i) != null) { up.add(down.get(i)); } } } return root; }