Binary Search Tree DFS Template

Two methods:

1. Traverse

2. Divide & Conquer

 // Traverse: usually do not have return value
 public class Solution {
     public void traverse(TreeNode root) {
         if (root == null)
             return;
         traverse(root.left);
         traverse(root.right);
     }
 }

 // Divide & Conquer: usually have return value
 public class Solution {
     public ResultType traversal(TreeNode root) {
         if (root == null) {
             // do something and return
         }

         // Divide
         ResultType left = traversal(root.left);
         ResultType right = traversal(root.right);

         // Conquer
         ResultType merge = Merge from left to right.
         return result;
     }
 }