94.二叉树的中序遍历.js

/*
 * @lc app=leetcode.cn id=94 lang=javascript
 *
 * [94] 二叉树的中序遍历
 *
 * https://leetcode-cn.com/problems/binary-tree-inorder-traversal/description/
 *
 * algorithms
 * Medium (67.87%)
 * Likes:    274
 * Dislikes: 0
 * Total Accepted:    58.1K
 * Total Submissions: 85.5K
 * Testcase Example:  '[1,null,2,3]'
 *
 * 给定一个二叉树，返回它的中序 遍历。
 *
 * 示例:
 *
 * 输入: [1,null,2,3]
 * ⁠  1
 * ⁠   \
 * ⁠    2
 * ⁠   /
 * ⁠  3
 *
 * 输出: [1,3,2]
 *
 * 进阶: 递归算法很简单，你可以通过迭代算法完成吗？
 *
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * 递归
 * @param {TreeNode} root
 * @return {number[]}
 */
var inorderTraversal = function(root) {
  if (!root) return [];
  var res = [];
  function backtrack(node, nums) {
    node.left && backtrack(node.left, nums);
    nums.push(node.val);
    node.right && backtrack(node.right, nums);
  }
  backtrack(root, res);
  return res;
};
// @lc code=end