cogrammers/Algorithm

Algorithm

What is inside this repo? Each folder contains a algorithm questions, and some test (if it is written in ruby).

On the top of each question, there is a brief description of the question, input output, difficulty level and related tags.

How to ran it? Java solution:

1. Open https://codepad.remoteinterview.io/pads in browser.
2. Pause the solution in the editor and hit "run" on the bottom.

Ruby solution:

1. Open the terminal and clone the folder.
2. Direct inside the folder and ran Rspec file.

Greedy

  track everything!

Easy

• Stock Price

Binary Search

input: an array of intergers and a target.
output: index position of the first/any/last of the given target.

Template

• First Position of Target
• Classical Binary Search
• Last Position of Target

Easy

• Search a 2D Matrix
• Find closest number in array
• closest Number In Sorted Array

Med

• First Bad Version
• Find Peak Element

Hard

• Smallest Rectangle Enclosing Black Pixels

Pool

• Recover Rotated Sorted ArrayList

Binary Tree & Divide Conquer

  public class TreeNode {
    public int value;
    public TreeNode left, right;
    public TreeNode(int) {
      this.value = int;
      this.left = this.right = null;
    }
  }

// for codepad
class MyCode {

  public static class TreeNode {
    public int val;
    public TreeNode left, right;
    public TreeNode(int num) {
      this.val = num;
      this.left = this.right = null;
    }

  }

  public static void main (String[] args) {
    TreeNode root = new TreeNode(2);
    root.left = new TreeNode(3);
    root.right = new TreeNode(4);
    System.out.println(root.val);
  }
}

  class TreeNode {
    constructor(num) {
      this.val = num;
      this.left = this.right = null;
    }
  }

  var root = new TreeNode(3);
  console.log(root.val);

class TreeNode
  attr_accessor :val, :left, :right
  def initialize(num)
    @val = num
    @left = @right = nil
  end
end

root = TreeNode.new(5)

puts root.val

Template

• Preorder Traversal
• Inorder Traversal
• Postorder Traversal

Easy

• Binary Tree Paths
• Minimum Subtree
• Flatten Binary Tree to Linked List
• Subtree with Maximum Average

Med

• Validate Binary Search Tree
• Lowest common Ancestor

Breath First Search

  public class TreeNode {
    public int value;
    public TreeNode left, right;
    public TreeNode(int) {
      this.value = int;
      this.left = this.right = null;
    }
  }

// for codepad
class MyCode {

  public static class TreeNode {
    public int val;
    public TreeNode left, right;
    public TreeNode(int num) {
      this.val = num;
      this.left = this.right = null;
    }

  }

  public static void main (String[] args) {
    TreeNode root = new TreeNode(2);
    root.left = new TreeNode(3);
    root.right = new TreeNode(4);
    System.out.println(root.val);
  }
}

  class TreeNode {
    constructor(num) {
      this.val = num;
      this.left = this.right = null;
    }
  }

  var root = new TreeNode(3);
  console.log(root.val);

class TreeNode
  attr_accessor :val, :left, :right
  def initialize(num)
    @val = num
    @left = @right = nil
  end
end

root = TreeNode.new(5)

puts root.val

Template

• Binary Tree Level Order Traversal
• Graph Valid Tree
• Zombie in Matrix

Depth First Search

Template

  Recursion:
    - Definition
    - Disassembly
    - Exit

Easy

• Combination Sum
• Combination Sum II
• Palindrome Partitioning
• Permutations

Linked List & Array

Template

public ListNode {
  int val;
  ListNode next;
  ListNode(int val) {
    val = val;
    next = null;
  }
}

• Reverse Order Storage
• Add Two Numbers
• Insert Into A Cyclic Sorted List

Two Pointers

Template

// reverse an array
// use while
public void reverse(char[] s) {
  int left = 0, right = s.length - 1;
  while (left < right) {
      char temp = s[left];
      s[left] = s[right];
      s[right] = temp;
      left++;
      right--;
  }
}

// use for loop
public void reverse(char[] s) {
    for (int i = 0, j = s.length - 1; i < j; i++, j--) {
        char temp = s[i];
        s[i] = s[j];
        s[j] = temp;
    }
}

Same direction two pointers questions:

• Remove Duplicates In An Array
• Window Sum
• Two Sum Difference Equals To Target
• Middle Of Linked List
• Linked List Cycle

Opposite direction two pointers questions:

• Two Sum Input Array Is Sorted
• Valid Palindrome
• Recover Rotated Sorted List
• Move Zeroes

Easy

• Two Sum Unique Pairs

Med

• Find All Anagrams In A String
• Sort Colors

Question Pool

• K Distinct Character
• Valid Parenthesis

Coding Style

Google Coding Style

Data Structures

How do we do this one?

1. We can vote the topic for the next meetup and do flash talk(15min?).
2. Have someone talks about it during the meetup.(more like a short class?? it may be really dry!)