Diameter of a Binary Tree

-
Problem is here: https://leetcode.com/problems/diameter-of-binary-tree/description/

Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.
Example:
Given a binary tree 
          1
         / \
        2   3
       / \     
      4   5
Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].
Note: The length of path between two nodes is represented by the number of edges between them.

If you know how to code the height of a binary tree, then you can solve this problem.

Here is the gist of the problem: just think about solving the height of a binary tree problem, which is the classic post-order traversal example:

Height(T)
  T is null ==> 0
  Else ==> Max(Height(T.L), Height(T.R)) + 1

The only difference is that along the calculation you'll be carrying over (by reference) a diameter variable. Before returning within the height function, you'll calculate the value of the diameter variable for the current node. And what's that value?
That value will be the Max between three values: the left diameter, the right diameter, and finally the height of the left node plus the height of the right node plus 1 (itself). Basically what we're saying is that the diameter for the current node is either the best diameter of its children, or the path going thru the node itself. This is all calculated in one line as seen in the code below.
That's it. Good execution time too. Cheers, Marcelo.


public class Solution
{
public int DiameterOfBinaryTree(TreeNode root)
{
int diameter = 0;
Height(root, ref diameter);
return diameter > 0 ? diameter - 1 : diameter;
}

private int Height(TreeNode root, ref int diameter)
{
if (root == null) return 0;

int leftDiameter = 0;
int leftHeight = Height(root.left, ref leftDiameter);
int rightDiameter = 0;
int rightHeight = Height(root.right, ref rightDiameter);

diameter = Math.Max(Math.Max(leftDiameter, rightDiameter), 1 + leftHeight + rightHeight);
return 1 + Math.Max(leftHeight, rightHeight);
}
}

Comments

  1. TarasJanuary 12, 2019 at 10:49 PM

    I love recursion :) My solution is very similar, although I try to avoid mutable parameters and return a struct with max diameter and depth.

    class Solution {
    private:
    struct Result { int diameter; int depth; };
    Result maxDiameterAndDepth(const TreeNode* root) const {
    if (root == nullptr) return {0, 0};
    auto leftResult = maxDiameterAndDepth(root->left);
    auto rightResult = maxDiameterAndDepth(root->right);
    return {
    max({leftResult.diameter, rightResult.diameter, leftResult.depth + rightResult.depth}),
    1 + max(leftResult.depth, rightResult.depth)
    };
    }
    public:
    int diameterOfBinaryTree(const TreeNode* root) const {
    return maxDiameterAndDepth(root).diameter;
    }
    };

    https://gist.github.com/ttsugriy/e1a3e2f4f61cfda6ad70c698ee10de8a

    Cheers,
    Taras

    ReplyDelete
  2. Marcelo De BarrosJanuary 12, 2019 at 10:58 PM

    👌👌👌👍👍👍👏👏👏

    ReplyDelete

Post a Comment

Popular posts from this blog

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:    Go's `map` is generally more effi
Read more

Claude vs ChatGPT: A Coder's Perspective on LLM Performance

-
Image
In the rapidly evolving world of Large Language Models (LLMs), recent releases from OpenAI's ChatGPT have garnered significant attention. However, when it comes to coding tasks, Anthropic's Claude.ai continues to impress me with its speed and quality of output. Benchmarking with LeetCode While LeetCode problems aren't the definitive measure of an AI's coding capabilities (they're pre-designed puzzles, after all), they offer an interesting playground for comparison. Let's dive into a recent example: The Problem K-th Largest Perfect Subtree Size in Binary Tree - LeetCode 3319. K-th Largest Perfect Subtree Size in Binary Tree Medium 36 6 Add to List Share You are given the  root  of a  binary tree  and an integer  k . Return an integer denoting the size of the  k th   largest   perfect binary   subtree , or  -1  if it doesn't exist. A  perfect binary tree  is a tree where all leaves are on the same level, and every parent has two children.   Example 1: Input:  
Read more

ProjectEuler Problem 719 (some hints, but no spoilers)

-
Image
Last time that I solved a ProjectEuler (PE) problem was in 2015... This is their latest problem as of today:  https://projecteuler.net/problem=719 Number Splitting        Problem 719 We define an  S S -number to be a natural number,  n n , that is a perfect square and its square root can be obtained by splitting the decimal representation of  n n  into 2 or more numbers then adding the numbers. For example, 81 is an  S S -number because  81 − − √ = 8 + 1 81 = 8 + 1 . 6724 is an  S S -number:  6724 − − − − √ = 6 + 72 + 4 6724 = 6 + 72 + 4 . 8281 is an  S S -number:  8281 − − − − √ = 8 + 2 + 81 = 82 + 8 + 1 8281 = 8 + 2 + 81 = 82 + 8 + 1 . 9801 is an  S S -number:  9801 − − − − √ = 98 + 0 + 1 9801 = 98 + 0 + 1 . Further we define  T ( N ) T ( N )  to be the sum of all  S S  numbers  n ≤ N n ≤ N . You are given  T ( 10 4 ) = 41333 T ( 10 4 ) = 41333 . Find  T ( 10 12 ) The rules of PE prevent me from disclosing the solution (they are very picky about it, rightfully so), but I can chat abo
Read more