/*
 * function TreeNode(x) {
 *   this.val = x;
 *   this.left = null;
 *   this.right = null;
 * }
 */

/**
  * 
  * @param root TreeNode类 
  * @return int整型
  */
function maxDepth( root ) {
    // write code here
    
    return dfs(root)
}
function dfs(root){
    if(root===null){
        return 0
    }
   let  left = dfs(root.left)
   let right = dfs(root.right)
   return  Math.max(left+1,right+1)
}
module.exports = {
    maxDepth : maxDepth
};