maximum-depth-of-binary-tree.js

/**Given the root of a binary tree, return its maximum depth.

A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

*/
/**
 * 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 maxDepth = function(root) {
    function dfs(node) {
      if (node === null) {
        return 0;
      }
      let leftH = dfs(node.left);
      let rightH = dfs(node.right);
      
      return 1 + Math.max(leftH, rightH);
      
    }
    
    return dfs(root);
      
  };