Exception in thread “main” java.lang.StringIndexOutOfBoundsException: String index out of range: 5 at java.lang.String.charAt(String.java:646)

Question

The following program is the GAME OF THRONES-1 problem from hackerrank. But I am facing the given error while executing. I would be grateful if anyone could help. The error would be:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 5
at java.lang.String.charAt(String.java:646)

This is my code

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;
import java.util.Arrays;

public class try123 
{
    public static void main(String[] args) 
    {
        Scanner myScan = new Scanner(System.in);
        String inputString = myScan.nextLine();
        String s=inputString;        //abccba
        String ans;     //YES or NO
        String A="";
        int flag=0;  
        String news="";
        String nrev="";
        String rev="";
        //char arr[]=new char[100000];
        char arr[]=inputString.toCharArray();
        Arrays.sort(arr);
        String b= new String(arr);   //sorted string

        int len=b.length();
        if((len%2)!=0)
        { 
            A=b.substring(len-1,len);

            len=len-1;
            b=b.substring(len-1);
            flag=1;
        }
        for(int l=(len-1);l>=0;l--)
        {
            rev=rev+b.charAt(l);
        }
        for(int i=1;i<len;i=i+2)  //len=6
        {
            news=news+b.charAt(i)+rev.charAt(i-1);
        }
        if(flag==1)
            news=news.substring(0,(len/2)-1)+A+news.substring((len/2),len-1);
        for(int o=(news.length()-1);o>=0;o--)
        {
            nrev=nrev+b.charAt(o);
        }
        if(news==nrev)
            ans="YES";
        else
            ans="NO";
        System.out.println(ans);  
        myScan.close();
    }
}

Answer 1

The problem seems to be here:

for(int i=1;i<len;i=i+2)  //len=6
{
    news=news+b.charAt(i)+rev.charAt(i-1);
}

You are increasing i by 2, so for even len values, you would exceed the character limit for your string (which is why you're seeing this exception come)

java.lang.StringIndexOutOfBoundsException: String index out of range

Answer 2

These lines leads you to the error :

    if ((len % 2) != 0) {
        A = b.substring(len - 1, len);
        len = len - 1;
        b = ;
        flag = 1;
    }
    for (int l = (len - 1); l >= 0; l--) {
        rev = rev + b.charAt(l);
    }

Before these lines, len is the length of b , on the third line, it becomes b's length - 1, and then you put in b b.substring(len - 1) , this means : the last 2 char of b. Now b is 2 character long, but len is still the original length - 1. Then you set int l = (len - 1) , and do b.charAt(l) . B is 2 character long and you try to access the l-th character, out of range.

Answer 3

The problem is here :

   if((len%2)!=0)
   { 
       A=b.substring(len-1,len);
       len=len-1;
       b=b.substring(len-1); // this returns a String with the last 2 characters of
                             // the original
       flag=1;
   }

When the input String has an odd length, you are keeping just the last two characters of that String.

I think you meant to remove only the last character of the String, which should be done like this :

   if((len%2)!=0)
   { 
       A=b.substring(len-1,len);    
       len=len-1;
       b=b.substring(0,len); // this would return the original String minus the last
                             // character
       flag=1;
   }