Binary Search Tree DFS Template

Two methods:
1. Traverse
2. Divide & Conquer
 1 // Traverse: usually do not have return value
 2 public class Solution {
 3     public void traverse(TreeNode root) {
 4         if (root == null)
 5             return;
 6         traverse(root.left);
 7         traverse(root.right);
 8     }
 9 }
10 
11 // Divide & Conquer: usually have return value
12 public class Solution {
13     public ResultType traversal(TreeNode root) {
14         if (root == null) {
15             // do something and return
16         }
17 
18         // Divide
19         ResultType left = traversal(root.left);
20         ResultType right = traversal(root.right);
21 
22         // Conquer
23         ResultType merge = Merge from left to right.
24         return result;
25     }
26 }