UCSD CSE Summer Series

Hi all!

Here with summer series updates!

🔗 Links and Resources

• Through our undergraduate committee, faculty around the department have open office hours for students to come by and talk about a variety of topics. Check ouf the table and the calendar on this page, which gets updated throughout the year.
• I continue to hold Remote Office Hours on Tuesdays at 11am pacific time for the rest of the summer. You can find the link through my contact page which has a calendar of many advising office hours!
• I got a few questions about tutoring, which is a role where undergraduates work for a course as an instructional assistant. Check out the CSE tutoring page for more details.

The website https://cse-summer-series.github.io/2025/ has all of the summer series messages.

✅ Do Now! (Do one, some, or all!)

• Watch the video about search tree checking:

  https://youtu.be/GBvzkgYFkiM

  This one looks at the key properties of binary search trees.

  https://leetcode.com/problems/validate-binary-search-tree/submissions/1752652924/

• Fill out the welcome form if you haven’t – if you have, you should have gotten an email from me by now saying hi and replying to your questions.

• Join the Discord server and say hi:

  https://discord.gg/4zexzTVv6Z

  I will also be posting assignment solutions given by students with some discussion to Discord.

• Do your best to complete the Recover Binary Search Tree problem in a programming language of your choice:

  https://leetcode.com/problems/recover-binary-search-tree/description/

• As another kind of review (and preparation for CSE29!) try taking my Java solution (below/in video) and translate it to a C solution. Review past videos to see how I approached tree programming with C structs and pointers.

• For either or both of those tasks, share your solution with me by replying to this email or putting the code in a direct message on Discord. I’ll share some answers that I see on Discord next week.

The code from today’s video is copied here for your reference:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isValidBST(TreeNode root) {
        if(root == null) { return true; }
        else {
            boolean leftIsBST = isValidBST(root.left);
            boolean rightIsBST = isValidBST(root.right);
            boolean leftAllSmaller = allSmaller(root.left, root.val);
            boolean rightAllLarger = allLarger(root.right, root.val);
            return leftIsBST && rightIsBST && leftAllSmaller && rightAllLarger;
        }
    }

    public boolean allLarger(TreeNode node, int val) {
        if(node == null) { return true; }
        else {
            if(node.val <= val) { return false; }
            return allLarger(node.left, val) && allLarger(node.right, val);
        }
    }

    public boolean allSmaller(TreeNode node, int val) {
        if(node == null) { return true; }
        else {
            if(node.val >= val) { return false; }
            return allSmaller(node.left, val) && allSmaller(node.right, val);
        }
    }
}