Java Coding Interview Problems with Solutions

Java Coding Interview Problems with Solutions

🔹 1. Reverse a String

Problem:

Reverse a given string.

Solution:

class Main {
    public static void main(String[] args) {
        String str = "hello";
        String rev = "";

        for (int i = str.length() - 1; i >= 0; i--) {
            rev += str.charAt(i);
        }

        System.out.println(rev);
    }
}

🔹 2. Check Palindrome

Problem:

Check if a string is palindrome.

Solution:

class Main {
    public static void main(String[] args) {
        String str = "madam";
        String rev = new StringBuilder(str).reverse().toString();

        if (str.equals(rev)) {
            System.out.println("Palindrome");
        } else {
            System.out.println("Not Palindrome");
        }
    }
}

🔹 3. Find Largest Number in Array

Solution:

class Main {
    public static void main(String[] args) {
        int[] arr = {10, 50, 30, 90, 20};
        int max = arr[0];

        for (int i = 1; i < arr.length; i++) {
            if (arr[i] > max) {
                max = arr[i];
            }
        }

        System.out.println("Largest: " + max);
    }
}

🔹 4. Find Smallest Number in Array

class Main {
    public static void main(String[] args) {
        int[] arr = {10, 50, 5, 90, 20};
        int min = arr[0];

        for (int i = 1; i < arr.length; i++) {
            if (arr[i] < min) {
                min = arr[i];
            }
        }

        System.out.println("Smallest: " + min);
    }
}

🔹 5. Fibonacci Series

Problem:

Print first N Fibonacci numbers.

class Main {
    public static void main(String[] args) {
        int n = 10;
        int a = 0, b = 1;

        for (int i = 1; i <= n; i++) {
            System.out.print(a + " ");
            int c = a + b;
            a = b;
            b = c;
        }
    }
}

🔹 6. Factorial of a Number

class Main {
    public static void main(String[] args) {
        int num = 5;
        int fact = 1;

        for (int i = 1; i <= num; i++) {
            fact *= i;
        }

        System.out.println("Factorial: " + fact);
    }
}

🔹 7. Check Prime Number

class Main {
    public static void main(String[] args) {
        int num = 7;
        boolean isPrime = true;

        for (int i = 2; i < num; i++) {
            if (num % i == 0) {
                isPrime = false;
                break;
            }
        }

        System.out.println(isPrime ? "Prime" : "Not Prime");
    }
}

🔹 8. Sum of Array Elements

class Main {
    public static void main(String[] args) {
        int[] arr = {10, 20, 30};
        int sum = 0;

        for (int num : arr) {
            sum += num;
        }

        System.out.println("Sum: " + sum);
    }
}

🔹 9. Count Vowels in String

class Main {
    public static void main(String[] args) {
        String str = "education";
        int count = 0;

        for (char c : str.toCharArray()) {
            if ("aeiou".indexOf(c) != -1) {
                count++;
            }
        }

        System.out.println("Vowels: " + count);
    }
}

🔹 10. Swap Two Numbers

class Main {
    public static void main(String[] args) {
        int a = 10, b = 20;

        int temp = a;
        a = b;
        b = temp;

        System.out.println(a + " " + b);
    }
}

🔹 11. Remove Duplicates from Array

import java.util.*;

class Main {
    public static void main(String[] args) {
        int[] arr = {1, 2, 2, 3, 4, 4};

        Set<Integer> set = new HashSet<>();
        for (int num : arr) {
            set.add(num);
        }

        System.out.println(set);
    }
}

🔹 12. Find Second Largest Number

class Main {
    public static void main(String[] args) {
        int[] arr = {10, 50, 30, 90, 20};

        int first = Integer.MIN_VALUE;
        int second = Integer.MIN_VALUE;

        for (int num : arr) {
            if (num > first) {
                second = first;
                first = num;
            } else if (num > second && num != first) {
                second = num;
            }
        }

        System.out.println("Second Largest: " + second);
    }
}

🔹 13. Check Armstrong Number

class Main {
    public static void main(String[] args) {
        int num = 153, temp = num, sum = 0;

        while (num > 0) {
            int digit = num % 10;
            sum += digit * digit * digit;
            num /= 10;
        }

        System.out.println(temp == sum ? "Armstrong" : "Not Armstrong");
    }
}

🔹 14. Reverse a Number

class Main {
    public static void main(String[] args) {
        int num = 1234;
        int rev = 0;

        while (num != 0) {
            rev = rev * 10 + num % 10;
            num /= 10;
        }

        System.out.println(rev);
    }
}

🔹 15. Check Even or Odd

class Main {
    public static void main(String[] args) {
        int num = 10;

        if (num % 2 == 0) {
            System.out.println("Even");
        } else {
            System.out.println("Odd");
        }
    }
}