题目传送：​​https://leetcode.cn/problems/maximum-depth-of-binary-tree/​​

运行效率

代码如下

public int maxDepth(TreeNode root) {
    //处理边界情况
    if(root==null){
      return  0;
    }
    //如果是叶子节点
    if(root.left==null&&root.right==null){
      return 1;
    }
    int leftHeight = maxDepth(root.left);
    int rightHeight = maxDepth(root.right);
    return Math.max(leftHeight, rightHeight)+1;
  }