JAVA Coding

Question 1

Swap values of two variables

Answer 1

public class Swap {
public static void main(String[] args) {
int j = 15;
int i = 10;

j = j - i; // j = 15 - 10; j = 5
i = i + j; // i = 10 + 5; i = 15
j = i - j; // j = 15 - 5; j = 10
System.out.println(i); // 15
System.out.println(j); // 10
}
}

Question 2

Two String Anagram

Answer 2

public static void main(String[] args)

System.out.println(isAnagtarm(“abc”, “cba”);
System.out.println(IsAnagram(“asd”, “zxc”);

public static boolean isAnagram(String str, String str1) {
char ch[] = str.toCharArray();
char ch1[] = str1.toCharArray();

Arrays.sort(ch);
Arrays.sort(ch1);

return Arrays.equals(ch, ch1);
}
}

Question 3

Prime Number

Answer 3

public static void main(String [] args) {

System.out.println(primeNum(7));
System.out.println(primeNum(24));
}
public static boolean primeNum(int num) {
for (int i = 2; i < num/2; i++) {
if (num % i == 0) {
return false;
}
return true;
}
}

Question 4

String reverse using StringBuilder

Answer 4

public String reverseStr(String str) {
// create variable to store reversed version of str
StringBuilder reverse = new StringBuilder();

// iterate over input string from the back with charAt
for(int i = str.length() - 1; i >= 0; i--) {
  // add chars to reversed variable
  reverse.append(String.valueOf(str.charAt(i)));
}

// convert to string and return reversed version 
return reverse.toString();   }

Question 5

Array reverse

Answer 5

public void revArr(int[] arrNum) {
// we will use two ‘pointers’. One pointer will start from the beginning
// another one from the back and we will swap their values

// pointer that will start from the back
int j = arrNum.length - 1;

// our loop will go till half of our input array
// 'i' is a pointer that will start from the beginning
for(int i = 0; i < arrNum.length / 2; i++) {
  // swap elements using positions of i and (j - i)
  int tmp = arrNum[i];
  arrNum[i] = arrNum[j - i];
  arrNum[j - i] = tmp;
}   }

Question 6

String palindrome

Answer 6

// isPal(“anna”) -> true
// isPal(“civic”) -> true
// isPal(“apple”) -> false
// isPal(“level”) -> true

public boolean isPal(String str) {
// we will use two ‘pointers’. One pointer will start looking from beginning
// another from the back. If values of pointers are not equal, we can return false

int j = str.length() - 1; // pointer for the back

// loop will go till half because we have two pointers
for(int i = 0; i < str.length() / 2; i++) {
  // if pointers values are not equal return false
  if(str.charAt(i) != str.charAt(j - i)){
    return false;
  }
}

// if program reach here, it means all values were equal so it's palindrome
return true;   }

Question 7

Reverse string

Answer 7

public class ReverseStr {
public static void main(String[] args) {
// Implement revStr(String str) method so
// it will return the reverse version of its str argument.
String res = revStr(“apple”);
System.out.println(res); // elppa
}

public static String revStr(String str) {
	String res = "";
	for (int k = str.length() - 1; k >= 0; k--) {
		str += str.charAt(k);
	}    	
	return str;           
} }

Question 8

Number palindrome

Answer 8

// isPalNum(545) -> true
// isPalNum(1001) -> true
// isPalNum(13) -> false
// isPalNum(33) -> true

public boolean isPalNum(int num) {
// there are two most important things to remember
// to get most right number, we can do ‘num % 10’
// to remove most right number, we can do ‘num / 10’
// both will work for any numbers

int copyOfOriginal = num;
int reversedNumber = 0;
int remainder;

while(num > 0) {
  // get most right number
  remainder = num % 10;

  // multiply by 10 to concat, not to add(plus)
  reversedNumber = (reversedNumber * 10) + remainder;

  // remove most right number from num. 
  num = num / 10;
}

// if reversed version and original are equal so it's palindrome
return reversedNumber == copyOfOriginal;   }

Question 9

Max number from an array

Answer 9

// max({4, 781, 8, 99, 103}) -> 781
// max({1, 2, 3, 4, 5}) -> 5
// max({3, 4}) -> 4
// max({100}) -> 100

public int max(int[] arrNum) {
// assume first element of array is biggest number
int max = arrNum[0];

// loop over the array and test our above assumption
for(int i = 0; i < arrNum.length; i++) {
  // if max was not the biggest number, update it
  if(max < arrNum[i]) {
    max = arrNum[i];
  }
}

// after the loop max variable will hold the biggest number
return max;                     }

Question 10

Min number from an array

Answer 10

// min({4, 781, 8, 99, 103}) -> 4
// min({1, 2, 3, 4, 5}) -> 1
// min({3, 4}) -> 3
// min({100}) -> 100

public int min(int[] arrNum) {
// assume first element of array is the smallest number
int min = arrNum[0];

// loop over the array and test assumption
for(int i = 0; i < arrNum.length; i++) {
  // if min was not smallest, update it
  if(min > arrNum[i]) {
    min = arrNum[i];
  }
}

return min;   }

Question 11

String reverse

Answer 11

public class Practice {
public static void main(String[] args) {
System.out.println(revStr(“apple”));
}
public static String revStr(String str) {
String rev = “”;
for (int i = str.length() - 1; i >= 0; i–) {
rev += str.charAt(i);
}
return rev;
}
}