My Programming Notes & Code Snippets

Accessing Cloudera's CDH using SSH

8:41 PM

Recently, I started learning Hadoop and practised MapReduce jobs on a linux distribution called CDH (Cloudera Distribution Including Apache Hadoop). It is an excellent VM loaded with Hadoop Ecosystem applications. This VM has CentOS as the operating system installed on it.

In this tutorial, I will walk through how to SSH the VM and run commands from your local terminal other than performing all the task inside the VM. I started to opt this methodology for practicing Hadoop because my VM used to freeze at times while working on Eclipse inside it (Due to limited RAM on my Machine).

To connect the VM with SSH, we require three things :
i) OpenSSH installed in the VM
ii) Firewall Disable in the VM
iii) Network Configuration of VirtualBox/VMware

Step I : Installing OpenSSH
Open terminal in the VM. Login in as root and install OpenSSH using following command:

yum -y install openssh-server

Once, OpenSSH has been installed, we can add this service to the startup by running following commands:

chkconfig sshd on

service sshd start

Finally, we can check if can check if OpenSSH is running on port 22 or not by following command.

netstat -tulpn | grep :22

Step II : Disable Firewall
The firewall can be disabled using following on the VM terminal :

service iptables stop
chkconfig iptables off

Step III : VirtualBox configuration
In the VirtualBox where the CDH VM image will be setup must have following Network settings.

Now, restart the Virtual Machine.

Once Virtual Machine is started, open terminal application inside it and run ifconfig on it.

It will provide you an IP address. Note down the IP Address.

Finally, run SSH command from your Host System to this IP address and login into the system.

ssh username@VM_IP_ADDRESS

To copy files from local system to virtual machine, use scp command from terminal in local system.

Copy file from local to VM:

scp local_file username@VM_IP_ADDRESS:/Directory_Location_on_VM

Copy file from VM to local:

scp username@VM_IP_ADDRESS:/File_location_on_VM/file_name

Compile your JAR/Class files from local system. Copy them to VM using scp and run the Hadoop job by logging into the VM from terminal using ssh and executing commands in the VM.

Triangle traversal to get maximum sum

7:46 PM

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class Problem_18 {
 private static int heightOfTree = 100;
 private final String fileName = "problem_67.in";
 private int[][] tree;

 public int maxValue() throws IOException {
  readTree();

  for (int i = Problem_18.heightOfTree - 2; i >= 0; i--)
   for (int j = 0; j <= i; j++)
    tree[i][j] += tree[i + 1][j] > tree[i + 1][j + 1] ? tree[i + 1][j] : tree[i + 1][j + 1];

  return tree[0][0];
 }

 private void readTree() throws IOException {
  tree = new int[Problem_18.heightOfTree][];

  BufferedReader bufferedReader = new BufferedReader(new FileReader(fileName));
  for (int i = 0; i < Problem_18.heightOfTree; i++) {
   tree[i] = new int[i + 1];
   String[] values = bufferedReader.readLine().split(" ");
   for (int j = 0; j <= i; j++)
    tree[i][j] = Integer.parseInt(values[j]);
  }
 }

 public static void main(String[] args) throws IOException {
  System.out.println(new Problem_18().maxValue());
 }
}

Autocomplete

Autocomplete with Google Maps API

3:41 AM

Sorting

Visual Bubble Sort

3:37 PM

Euler

Triangle Travarsal in stepwise order and calculation of maximum sum

11:41 AM

ORIGINAL PROBLEM By starting at the top of the triangle and moving to adjacent numbers on the row below, the maximum total from top to bottom is 27.
5
9 6
4 6 8
0 7 1 5

I.e. 5 + 9 + 6 + 7 = 27. Write a program in a language of your choice to find the maximum total from top to bottom in triangle.txt, a text file containing a triangle with 100 rows.

This problem is popularly known as Euler's 67th problem . The logic is that starting from second last row, find the max of two adjacent values (of next row that) can be reached. Once we find the max, for each item of the row, add the max value to the row value. This will eliminate the last row. Now, we can work our way backwards, i.e to the top. Note that as we move upwards the triangles, the number of rows reduces, till we reach the top. Once we reach 2nd row from top, adding the top value to the max of two values,
of the 2nd row, we get our answer.

Solution
Place the text file "triangle.txt" in D drive of your computer else change path accordingly in code.
triangle.txt

SOURCE CODE in Java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class Traingular_Sum {
private static int heightOfTriangle = 100;
private final String fileName = "D://triangle.txt";
private int[][] triangle;

public int maxValue() throws IOException {
readTriangle();

for (int i = Traingular_Sum.heightOfTriangle - 2; i>= 0; i--)
for (int j = 0; j<= i; j++) 
triangle[i][j] += triangle[i + 1][j] > triangle[i + 1][j + 1] ? triangle[i + 1][j] : triangle[i + 1][j + 1];

return triangle[0][0];
}

private void readTriangle() throws IOException {
triangle = new int[Traingular_Sum.heightOfTriangle][];

BufferedReader bufferedReader = new BufferedReader(new FileReader(fileName));
for (int i = 0; i < Traingular_Sum.heightOfTriangle; i++) {
triangle[i] = new int[i + 1];
String[] values = bufferedReader.readLine().split(" ");
for (int j = 0; j <= i; j++)
triangle[i][j] = Integer.parseInt(values[j]);
}
}

public static void main(String[] args) throws IOException {
System.out.println(new Traingular_Sum().maxValue());
}
}

My Programming Notes & Code Snippets

Accessing Cloudera's CDH using SSH

Triangle traversal to get maximum sum

Autocomplete with Google Maps API

Visual Bubble Sort

Triangle Travarsal in stepwise order and calculation of maximum sum

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