Template 1: Traverse

public class Solution {

public void traverse\(TreeNode root\) {

    if \(root == null\) {

        return;

    }

    // do something with root

    traverse\(root.left\);

    // do something with root

    traverse\(root.right\);

    // do something with root

}

}

Tempate 2: Divide & Conquer

public class Solution {

public ResultType traversal\(TreeNode root\) {

    // null or leaf

    if \(root == null\) {

        // do something and return;

    }



    // Divide

    ResultType left = traversal\(root.left\);

    ResultType right = traversal\(root.right\);



    // Conquer

    ResultType result = Merge from left and right.

    return result;

}

}