Java Lambda Expressions HackerRank solution with Explanation

Lambda Expressions in Java

What is Lambda Expression?

Lambda expression is just anonymous function or we can say nameless function. 

• Lambda Expression in Java 8 with examples  

Problem Description :

Write the following methods that return a lambda expression performing a specified action:

1. PerformOperation isOdd(): The lambda expression must return true if a number is odd or false if it is even.
2. PerformOperation isPrime(): The lambda expression must return  if a number is prime or  if it is composite.
3. PerformOperation isPalindrome(): The lambda expression must return  if a number is a palindrome or  if it is not.

See full description on HackerRank :

• Java Lambda Expressions Probelm Description 

Sample Input and Output :

Input

1 4
2 5
3 898
1 3
2 12

Output

EVEN
PRIME
PALINDROME
ODD
COMPOSITE

The first integer specifies the condition to check for (1 for Odd/Even, 2 for Prime, or 3 for Palindrome). The second integer denotes the number to be checked.

So lets jump on solution

import java.io.*;
import java.util.*;

interface PerformOperation {
    boolean check(int a);
}

class MyMath {
    public static boolean checker(PerformOperation p, int num) {
        return p.check(num);
    }

    public PerformOperation isOdd() {
        return (num) -> (num % 2 != 0);
    }

    public PerformOperation isPrime() {
        return (num) -> {
            for (int i = 2; i <= num / 2; i++) {
                if (num % i == 0) {
                    return false;
                }
            }
            return true;
        };
    }

    public PerformOperation isPalindrome() {
        return (num) -> {
            String str = num + "";
            String newStr = new StringBuffer(str).reverse().toString();
            return str.equals(newStr);
        };
    }

}

public class Solution {

    public static void main(String[] args) throws IOException {
        MyMath ob = new MyMath();
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int T = Integer.parseInt(br.readLine());
        PerformOperation op;
        boolean ret = false;
        String ans = null;
        while (T-- > 0) {
            String s = br.readLine().trim();
            StringTokenizer st = new StringTokenizer(s);
            int ch = Integer.parseInt(st.nextToken());
            int num = Integer.parseInt(st.nextToken());
            if (ch == 1) {
                op = ob.isOdd();
                ret = ob.checker(op, num);
                ans = (ret) ? "ODD" : "EVEN";
            } else if (ch == 2) {
                op = ob.isPrime();
                ret = ob.checker(op, num);
                ans = (ret) ? "PRIME" : "COMPOSITE";
            } else if (ch == 3) {
                op = ob.isPalindrome();
                ret = ob.checker(op, num);
                ans = (ret) ? "PALINDROME" : "NOT PALINDROME";

            }
            System.out.println(ans);
        }
    }
}

Solution Explanation :

• We need to create three new functions 1. isOdd() 2. isPrime() 3. isPalindrome().
• In isOdd() function, we have to check given number is odd or not. So basically if number is divisable by 2 it means number is not Odd so return false otherwise true.
• In isPrime() function, We have to check number is prime or not. A prime number is a number that is divisible by only two numbers: 1 and itself. So, if any number is divisible by any other number, it is not a prime number.
  
• we are looping from 2 to num/2. It is because a number is not divisible by more than its half. 
• In isPalindrome() function, We have to check number is palindrome or not. A palindrome number is a number that is same after reverse.
• For that we are storing num as String. After that reverse that number using StringBuffer reverse() method. and check both number using equals() method.

Happy Coding...

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