**Problem:**

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

**Solution:**

DFS

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int maxDepth(TreeNode root) {
return maxDepth(root, 0);
}
private int maxDepth(TreeNode root, int current) {
if (root == null) return current;
return Math.max(maxDepth(root.left, current + 1), maxDepth(root.right, current + 1));
}
}

*Related*