static class TreeNode{int val;TreeNode left;TreeNode right;int deep;}/*** 二叉树的前序遍历，RLR 根左右* @param root* @param res*/static void accessTree1(TreeNode root,List<Integer> res){if(root == null){return;}res.add(root.val);accessTree1(root.left,res);accessTree1(root.right,res);}/*** 二叉树的中序遍历，LRR 左根右* @param root* @param res*/static void accessTree2(TreeNode root,List<Integer> res){if(root == null){return;}accessTree2(root.left,res);res.add(root.val);accessTree2(root.right,res);}/*** 二叉树的后序遍历，LRR 左右根* @param root* @param res*/static void accessTree3(TreeNode root,List<Integer> res){if(root == null){return;}accessTree3(root.left,res);accessTree3(root.right,res);res.add(root.val);}public static void main(String[] args) {TreeNode node1 = new TreeNode();TreeNode node2 = new TreeNode();TreeNode node3 = new TreeNode();TreeNode node4 = new TreeNode();TreeNode node5 = new TreeNode();TreeNode node6 = new TreeNode();TreeNode node7 = new TreeNode();node1.val = 1;node2.val = 2;node3.val = 3;node4.val = 4;node5.val = 5;node6.val = 6;node7.val = 7;node1.left = node2;node2.left=node4;node2.right=node5;node1.right = node3;node3.left = node6;node6.left = node7;List<Integer> res = new ArrayList<>();accessTree1(node1,res);System.out.println("先序遍历："+res);res.clear();accessTree2(node1,res);System.out.println("中序遍历："+res);res.clear();accessTree3(node1,res);System.out.println("后序遍历："+res);res.clear();}