0222.完全二叉树的节点个数

/**
 * 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 countNodes = function (root) {
  let ret = 0;
  const dfs = (node) => {
    if (!node) return;
    ret++;
    dfs(node.left);
    dfs(node.right);
  };
  dfs(root);
  return ret;
};

/**
 * 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 countNodes = function (root) {
  if (!root) return 0;
  let ret = 0;
  const queue = [root];
  while (queue.length > 0) {
    const node = queue.shift();
    ret++;
    if (node.left) queue.push(node.left);
    if (node.right) queue.push(node.right);
  }
  return ret;
};