JAVA PRACTICE EXAM

JAVA PRACTICE  EXAM
Know that how good you are in programming

Problem A [Two’s Power]
Write a program that reads an integer n and checks whether n is a power of 2 (powers of 2 are 1,2,4,8,16,32, …). The output of your program is either “yes” or “no”.

public class LAU1
{
  public static void main (String[] args)
  {
    java.util.Scanner scan = new java.util.Scanner(System.in);
    int n = scan.nextInt();
    while (n >= 2)
    {
      if(n%2 != 0)
        break;
      if (n%2 == 0)
        n/=2;
    }
    
    if (n == 1) System.out.println("yes");
    else
      System.out.println("no");
  }
} 
Problem B [No Duplicates]
Write a program that read a string str and prints a string obtained from str by removing/ignoring duplicates. For example, if str is abbacdcae, then your program prints abcde. In other words, only the first occurrence of a character is printed.
 


import java.util.Scanner;

public class LAU2
{
  public static void main (String[] args)
  {
    String target = "";
    Scanner scan = new Scanner (System.in);
    String S = scan.nextLine();
    for (int i =0;i<S.length();i++)
    {
      boolean so = true;
      for (int j = 0 ; j<i;j++)
      {
        if (S.charAt(i) == S.charAt(j))
          so = false;
      }
      if (so) target += S.charAt(i);

    }
    
    System.out.print(target);
  }
}



Problem C [Integer Mirror]
Write a program that reads an integer N followed by N positive integers. For each entered integer, your program prints (on a new line) its digits in reverse. For example:
Input                          
3                                 
35423                         
7                                 
98710789
Output
32453
7
98701789


  import java.util.Scanner;
public class LAU3
{
  public static void main (String[] args)
  {
    Scanner scan = new Scanner (System.in);
    int N  = scan.nextInt();
    String[] nums = new String[N];
    for (int i =0;i<N;i++)
    {
      nums[i] = scan.next();
    }
    
    for (int i = 0;i<N;i++)
    {
      for (int j =nums[i].length()-1;j>=0;j--)
      {
        System.out.print(nums[i].charAt(j));
      }
      System.out.println();
    }
  }
}



Problem D [Prime Frequency]
Write a program that reads positive integers from the keyboard until the user enters 0. Then the program prints the number of prime numbers entered. Here is a sample:
Input                           Output


2 3 5 0                         3



public class LAU4
{
  public static boolean isPrime(int n)
  {
    if(n ==0 || n == 1 )
      return false;
    for (int i =2;i<n;i++)
    {
      if (n%i == 0)
        return false;
    }
    return true;
  }
  public static void main (String[] args)
  {
    java.util.Scanner scan = new java.util.Scanner(System.in);
    int i = -1;
    int count = 0;
    while ( i != 0)
    {
      i = scan.nextInt();
      if (isPrime(i)) count++;
    }
    System.out.println(count);
  }
  
}


Problem E [Palindromes]

Write a program that reads an integer N followed by N strings. For each string, your program prints yes or no according whether the string is a palindrome or not. Here is a sample:

3
kayak                           yes
palindrome                    no
wow                             yes
Input                           Output


public class LAU5
{
  public static boolean isPalindrome(String str)
  {
    for (int i = 0;i<str.length()-1;i++)
    {
      if (str.charAt(i) == str.charAt(str.length()-1-i))
        return true;
    }
    return false;
  }
  public static void main (String[] args)
  {
    java.util.Scanner scan = new java.util.Scanner(System.in);
    int N = scan.nextInt();
    
    for (int i =0;i<N;i++)
    {
      String temp = scan.next();
      if (isPalindrome(temp)) System.out.println("yes");
      else
        System.out.println("no");
        
    }
  }
}



Problem F [Flipped Star Triangles]
Complete the following program by writing the method starTriangle that takes an integer i and draws a flipped triangle (as shown below) of height i that is filled with stars. The main method (below) calls starTriangle N times, each time with one of the numbers between 1 and N. For example, if N is 3, the program calls starTriangle 3 times and prints:
                  
*****
 ***
   *

public static void main(String[] args) {
      Scanner input = new Scanner(system.in);
int N = input.nextInt();
for(int i = 1; i <= N; i++){
            starTriangle(i);
            System.out.println();
      }
}


Problem G [Fibonacci Number]
Complete and submit the following program by writing the boolean method isFib, which takes a positive integer n and checks whether n is one of the Fibonacci numbers (1,1,2,3,5,8,13,…).


public class FibNum

Input                           Output
3
2                                  yes
10                                No
13                                Yes

 
{
public static boolean isFib(int n)
{
}

public static void main(String[] args)
{
                                Scanner input = new Scanner(System.in);
int n, testnums = input.nextInt();
                                for(int j = 1; j <= testnums; j++)
{
n = input.nextInt();
if(isFib(n))
System.out.println(“Yes”);
else         System.out.println(“No”);
       
}
}
}


import java.util.Scanner;

public class LAU7
{
public static boolean isFib(int n)
{ 
  int a = 1; 
  int b =1;
  int c = 0;
  for (int i = 0;c<=n;i++)
  {
    c = a+b;
    a = b;
    b = c;
  if (c==n)
    return true;
  }
  return false;
}

public static void main(String[] args)
{
    Scanner input = new Scanner(System.in);
int n, testnums = input.nextInt();
    for(int j = 1; j <= testnums; j++)
{
n = input.nextInt();
if(isFib(n))
System.out.println("Yes");
else   System.out.println("No");
        
}
}
}


Problem H [Longest Natural Successors]
Two consecutive integers are natural successors if the second is the successor of the first in the sequence of natural numbers (1 and 2 are natural successors). Write a program that reads a number N followed by N integers, and then prints the length of the longest sequence of consecutive natural successors. Example:
Input                                     Output
7 2 3 5 6 7 9 10                       3

import java.util.Scanner;

public class LAU8
{
  public static void main (String[] args)
  {
    Scanner scan = new Scanner (System.in);
    int N = scan.nextInt();
    int[] nums = new int[N];
    for (int i =0;i<N;i++)
    {
      nums[i] = scan.nextInt();
    }
    int MAX = 0;
    int count = 0;
    for (int i =0;i<N-1;i++)
    {
      if (nums[i] + 1 == nums[i+1])
      {
        count+=1;
        if (count > MAX)
          MAX = count;
      }
      
      if (nums[i] + 1  != nums[i+1])
      {
        count = 0;
      }
      
    }
    if (MAX == 0) MAX = -1;
    System.out.println(MAX+1);
  }
}

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