写一个树

// 定义二叉树节点
function TreeNode(val, left, right) {this.val = (val === undefined ? 0 : val)this.left = (left === undefined ? null : left)this.right = (right === undefined ? null : right)
}// 示例使用
const root = new TreeNode(1,new TreeNode(2,new TreeNode(4),new TreeNode(5)),new TreeNode(3,null,new TreeNode(7))
);

二叉树的中序遍历

https://leetcode.cn/problems/binary-tree-inorder-traversal/description/

递归

/*** Definition for a binary tree node.* function TreeNode(val, left, right) {*     this.val = (val===undefined ? 0 : val)*     this.left = (left===undefined ? null : left)*     this.right = (right===undefined ? null : right)* }*/
/*** @param {TreeNode} root* @return {number[]}*/
var inorderTraversal = function(root) {const res = [];const inorder = (root) => {if (!root) {return;}inorder(root.left);res.push(root.val);inorder(root.right);}inorder(root);return res;
};

二叉树的先序遍历

var inorderTraversal = function(root) {const res = [];const inorder = (root) => {if (!root) {return;}res.push(root.val);inorder(root.left);inorder(root.right);}inorder(root);return res;
};

二叉树的后序遍历

var inorderTraversal = function(ro