LeetCode 题解：226. 翻转二叉树，递归，JavaScript，详细注释

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
function recursion(node) {
  // 如果当前节点不存在，则退出递归
  if (!node) {
    return;
  }
  // 将子节点互换
  const temp = node.left;
  node.left = node.right;
  node.right = temp;
  // 遍历互换后的子节点
  recursion(node.left);
  recursion(node.right);
}
/**
 * @param {TreeNode} root
 * @return {TreeNode}
 */
var invertTree = function (root) {
  // 递归遍历节点，并进行翻转
  recursion(root);
  return root;
};