LeetCode 104. 二叉树的最大深度

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/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var maxDepth = function (root) {
  if (!root) return 0;
  return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
};

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/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var maxDepth = function (root) {
  if (!root) return 0;
  const queue = [root];
  let res = 1;

  while (queue.length) {
    let len = queue.length;

    while (len) {
      const node = queue.shift();
      if (node.left) queue.push(node.left);
      if (node.right) queue.push(node.right);
      len--;
    }

    if (queue.length) res += 1;
  }
  return res;
};