输出单层节点

package 输出单层节点; class ListNode { int val; ListNode next = null; ListNode(int val) { this.val = val; } } class TreeNode { int val = 0; TreeNode left = null; TreeNode right = null; public TreeNode(int val) { this.val = val; } } public class TreeLevel { public ListNode p; public ListNode getTreeLevel(TreeNode root, int dep) { ListNode head = new ListNode(-1); p = head; preOrder(root, dep); return head.next; } private void preOrder(TreeNode root, int dep) { if (root == null || dep == 0) { return; } if (dep == 1) { p.next = new ListNode(root.val); p = p.next; } preOrder(root.left, dep - 1); preOrder(root.right, dep - 1); } public static void main(String[] args) { TreeNode root = new TreeNode(1); TreeNode left1 = new TreeNode(2); TreeNode right1 = new TreeNode(3); TreeNode left2 = new TreeNode(4); root.left = left1; root.right = right1; left1.left = left2; TreeNode right2 = new TreeNode(5); left1.right = right2; print(new TreeLevel().getTreeLevel(root, 1)); } private static void print(ListNode root) { if (root == null) { return; } else { System.out.print(root.val + " "); print(root.next); } } }