palindrome of a string in java

Question

The constraint of the question is that: The first line contains two integers N and LN, denoting the number of person and L,the maximum length of a person's name in Palindrome respectively. The ith of the next N lines contains a single string S denoting the name of the ith person. They can do that by choosing at most two non-overlapping substrings of their own name and reversing them.

My code is compiled properly but is giving run time error: So what needs to be changed? here is my code:

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Arrays;

class Palindrome {

    public static void main(String args[]) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        {
            String line = br.readLine();
            int N = Integer.parseInt(line);
            int l = Integer.parseInt(line);
            String a[] = new String[N];
            int c = 0;

            for (int i = 0; i < N; i++) {
                System.out.println("Enter names");
                a[i] = br.readLine();
            }
            String reverse[] = new String[N];

            int arrayLength = a.length;

            for (int i = arrayLength - 1; i >= 0; i--) {
                reverse[i] = reverse[i] + a[i].charAt(i);
            }
            if (Arrays.equals(a, reverse)) //if (a[i].equals(reverse[i]))
            {
                c++;

                System.out.println(c);

            }
        }
    }
}

I need to print the number of persons that can change their name to Palindrome form.

Example:

Input:        
   4 10            
   aacbaac
   acbdabc
   abcdcba
   abcbd

and

output:
   3

here 4 denotes total number of person 10 denotes the maximum length of each person name

output is 3 as only first 3 person can change their name to its respective form..

Answer 1

One issue you have is that you defined a string array, but you're trying to pass characters into it. You should make String reverse[] =new String[N]; into Char reverse[] =new Char[N];

Also, this reverse[i] = reverse[i] + a[i].charAt(i); should just be reverse[i] = a[i].charAt(i);

Answer 2

I presume this is a Codechef problem. The primary problem in your code is in the part where you assign the values to N and l . Notice that you take the input in line just once and then assign it's integer value to both N and l . So, the problem is that your program is not taking an expected input : you have to take the input in line twice . Change that part to

String line = br.readLine();
int N = Integer.parseInt(line);
line = br.readLine(); //add this line before assigning l's value
int l= Integer.parseInt(line);

Besides, what you are trying to do in the loop while finding the reverse of the string should be done in a nested loop construct. To abandon that complication, forget the second reverse array; you can use this one line statement to check for a palindrome string:

for(int i=0; i<a.length; i++){
    if(String.valueOf(new StringBuffer(a[i]).reverse()).equalsIgnoreCase(a[i]))
        //a[i] is a palindrome, do whatever you want to
}

Answer 3

Pass it to a StringBuilder inorder to reverse it. Review the code below:

   public static void main(String args[]) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String line = br.readLine();
        int N = Integer.parseInt(line);
        int l = Integer.parseInt(line);
        String a[] = new String[N];
        int c = 0;

        for (int i = 0; i < N; i++) {
            System.out.println("Enter names");
            a[i] = br.readLine();
        }
        String reverse[] = new String[N];

        int arrayLength = a.length;

        for (int i = arrayLength - 1; i >= 0; i--) {

            StringBuilder build = new StringBuilder(a[i]);

            reverse[i] = build.reverse().toString();
            if (a[i].equals(reverse[i])) {
                c++;
            }

        }
        System.out.println("Pal is " + c);

    }

I don't know what you are using the int variable l for, but modify it like I have done above with the N .