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);   } }