104. Maximum Depth of Binary Tree

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     public int maxDepth(TreeNode root) {
12         if (root == null)
13             return 0 ;
14         int depth = 0 ;
15         TreeNode node = null ;
16         Queue<TreeNode> que = new LinkedList<TreeNode>() ;
17         que.offer(root) ;
18         while(!que.isEmpty()){
19             int size = que.size() ;
20             for (int i = 0 ; i < size ; i++){
21                 node = que.poll() ;
22                 if (node.left != null){
23                     que.offer(node.left) ;
24                 }
25                 if (node.right != null){
26                     que.offer(node.right) ;
27                 }
28                 
29             }
30             depth++ ;
31         }
32         return depth;
33     }
34 }

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     public int maxDepth(TreeNode root) {
12         if (root == null)
13             return 0 ;
14         
15         return Math.max(maxDepth(root.left),maxDepth(root.right)) + 1 ;
16     }
17 }