Solving 450 LeetCode Problems

-
I'm a big believer that you should do what you like to do, what you're passionate about. 

One of my hobbies is LeetCode. I say as a hobby because that's what it really is: there is no expectation from my part that these problems will help me professionally (if one day they do, that's a bonus). I truly just do it because I enjoy - just as if you like playing video games, you should then just play. Just be happy :) 

Today I got to my 450th solved problem (over a couple of years now). The problem was to "find the leaves on a binary tree, and keep removing them and finding new leaves": https://leetcode.com/submissions/detail/271722558/

The solution is to literally just do that: find the leaves (DFS), remove them (that's why you need to pass the parent node along), and repeat until all the nodes are gone. On average the execution time will actually be NLogN since at every point you remove 1/2 the tree but you still need to traverse all nodes, hence NLogN. Code is below, cheers, ACC.


public class Solution
{
    public IList<IList<int>> FindLeaves(TreeNode root)
    {
        List<IList<int>> retVal = new List<IList<int>>();
        while (root != null)
        {
            List<int> list = new List<int>();
            TreeNode parent = null;
            FindLeavesAndDelete(ref parent, true, ref root, list);
            retVal.Add(list);
        }

        return retVal;
    }

    private void FindLeavesAndDelete(ref TreeNode parentNode,
                                        bool isRightNode,
                                        ref TreeNode node,
                                        IList<int> list)
    {
        if (node == null) return;
        if (node.left == null && node.right == null)
        {
            list.Add(node.val);
            if (parentNode != null)
            {
                if (isRightNode)
                {
                    parentNode.right = null;
                }
                else
                {
                    parentNode.left = null;
                }
            }
            else
            {
                node = null;
            }
            return;
        }
        if (node.left != null)
        {
            FindLeavesAndDelete(ref node,
                                false,
                                ref node.left,
                                list);
        }
        if(node.right != null)
        {
            FindLeavesAndDelete(ref node,
                                true,
                                ref node.right,
                                list);
        }
    }
}

Comments

Post a Comment

Popular posts from this blog

Advent of Code - Day 6, 2024: BFS and FSM

-
Image
To solve this Advent of Code (parts 1 and 2), I used Breadth-First Search (BFS) to keep moving the guard as well as Finite State Machine (FSM) to control the directions. This solves part 1 easily. Part 2 can be solved using the same technique, takes a little longer since you need to try every empty cell, but it eventually does the trick (takes a min or so). Code is down below, cheers, ACC. Day 6 - Advent of Code 2024 using System.IO; using System.Collections; using System; using System.Text; using System.Text.RegularExpressions; using System.ComponentModel.DataAnnotations; Process2(); void Process() { string fileName = "input.txt"; FileInfo fileInfo = new FileInfo(fileName); StreamReader sr = fileInfo.OpenText(); List map = new List (); int startRow = 0; int startCol = 0; while (!sr.EndOfStream) { string line = sr.ReadLine().Trim(); map.Add(new StringBuilder(line)); int indexStart = line.IndexOf('^'); ...
Read more

Golang vs. C#: performance characteristics (simple case study)

-
Image
This is an interesting example to study the performance characteristics of Golang compared to C# for a very particular case (not generalized though).  The same code was written in C# and Golang (literally translated from one to the other). Below you'll be able to see the source code for both. The problem is a simple post-order DFS in a tree-like graph. The code in C# times out (TLE = Time Limited Exceeded). The code in Golang not only works but beats 100% of the other Golang submissions. Take a look the image below: Some potential reasons for the performance gains from Go in this particular example are: 1. Language and Runtime Differences:    Go is compiled directly to machine code, while C# typically runs on a virtual machine (CLR).    Go has a simpler runtime with less overhead compared to the .NET runtime.    Go's garbage collector is designed for low latency, which can lead to better performance in some scenarios. 2. Data Structures:    G...
Read more

Advent of Code - Day 7, 2024: Backtracking and Eval

-
Image
Problem today requires backtracking and eval (evaluating a mathematical expression in the format of a string). Glad that it used a left-2-right evaluation, makes for an easy parsing and not overly complicated evaluation function. Code is down below for parts 1 and 2. Cheers, ACC. Day 7 - Advent of Code 2024 using System.IO; using System.Collections; using System; using System.Text; using System.Text.RegularExpressions; using System.ComponentModel.DataAnnotations; Process2(); void Process() { string fileName = "input.txt"; long retVal = 0; FileInfo fileInfo = new FileInfo(fileName); StreamReader sr = fileInfo.OpenText(); while (!sr.EndOfStream) { string line = sr.ReadLine().Trim(); string[] parts1 = line.Split(':'); long target = Int64.Parse(parts1[0]); string[] numbers = parts1[1].Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries); if (TryAll1(numbers, target, "", 0)) r...
Read more