Basic Code

1.  Find the top 3 elements of an array, Do not use sorting use 3 variables.
(Amazon Interview Question)
public class LargeNumberArray {
 public static void main(String args[]){
   int a[]={7,2,8,1,3,5,10,0,12,11};
   int large=a[0],second=a[0],third=a[0];
   int index=0,index1=0,index2=0;
   for (int i=0;i<a.length;i++)
   {
     if(a[i]>=large)
     {
        large=a[i];
        index=i;  
     }
   }
   for (int i=0;i<a.length;i++)
   {
      if(a[i]<large && a[i]>second))
      {
         second=a[i];
         index1=i;
      }
    }
   for (int i=0;i<a.length;i++)
   {
      if(a[i]<second && a[i]>third))
      {
         third=a[i];
         index2=i; 
      }
   }
   System.out.println("Large Number: "+large+ " Index: "+index);
   System.out.println("Large Number: "+second+ " Index: "+index1);
   System.out.println("Large Number: "+third+ " Index: "+index2);
  }
}

2.  Program for Fibonacci series.
import java.io.*;
public class Fibonacci {
public static void main(String args[])throws Exception
{
InputStreamReader ir=new InputStreamReader(System.in);
BufferedReader br=new BufferedReader(ir);
System.out.println("Enter Number: ");
String s=br.readLine();
int n=Integer.parseInt(s);
System.out.print("Series=");
fibonacci(n);
}
public static void fibonacci(int n)
{
int a=0,b=1;
for(int i=0;i<n;i++)
{
System.out.print(a+", ");
a=a+b;
b=a-b;
}
}
}

3. Program to check Palindrome Number.
import java.io.*;
public class Pallendrome {
public static void main(String[] args) throws Exception
{
InputStreamReader ir=new InputStreamReader(System.in);
BufferedReader br=new BufferedReader(ir);
System.out.print("Enter Number: ");
String s=br.readLine();
int n=Integer.parseInt(s);
palindrome(n);
}
public static void palindrome(int n)
{
int temp,reversed=0;
int number=n;
while(number>0)
{
temp=number%10;
number=number/10;
reversed=(reversed*10)+temp;
}
if (n==reversed)
{
System.out.println(n +"is Pallendrome") ;
}
else
{
System.out.println("Number is not Pallendrome "+ reversed) ;
}
}
}

4. Program to Reverse a string.
import java.io.*;
public class ReverseString {
public static void main(String args[])throws Exception
{
  InputStreamReader ir=new InputStreamReader(System.in);
BufferedReader br=new BufferedReader(ir);
System.out.print("Enter Number: ");
String s=br.readLine();
char c[]=s.toCharArray();
int length=c.length-1;
int l=0;
char j[]=new char[c.length];
for(int i=length;i>=0;i--)
{
j[i]=c[l];
l++;
}
String st = new String(j);
System.out.println("Reversed String: "+st);
}
}

5. How to find duplicate words in a string.

import java.util.*;
public class DupSearch {
    public static void main(String args[]){
        String s="a b f e a sd g t y uf s a b d x e c ";
        List<String> list = Arrays.asList(s.split(" "));
        Set<String> uniqueWords = new HashSet<String>(list);
        for (String word : uniqueWords) {
            System.out.println(word + ": " + Collections.frequency(list, word));
        }
    }
}

6. Swap two numbers by using two variables use exception handling and function. 

import java.io.*;

public class Swapping {
public static void main(String args[])throws Exception{
    swap();
}
public static void swap()throws Exception{
    InputStreamReader ir=new InputStreamReader(System.in);
    BufferedReader br= new BufferedReader(ir);
    try{
        System.out.print("Enter the Value of A= ");
        String s=br.readLine();
        int a=Integer.parseInt(s);
        System.out.println("A= "+a);
        System.out.print("Enter the Value of B= ");
        String s2=br.readLine();
        int b=Integer.parseInt(s2);
        System.out.println("B= "+b);
        a=a*b; // a=12
        b=a/b; // b=3
        a=a/b; // a=4
        System.out.println("**** Swapping the values ****");
        System.out.println("A=> "+a);
        System.out.println("B=> "+b);
    }
    catch (NumberFormatException e){
        System.out.println("Please Enter valid Number");
        swap();
    }
}
}