Episode 6 - Reverse an array using recursion

[sudiptapradhan]

There seems to be some problem with the java code for episode 6, would be great if you could look into it.
Thankyou

[UnresolvedCold]

Yes there are 2 mistakes.

1. ArrayList doesn't has length() as an inbuilt method.
2. arr.get(l) = arr.get(r) is not a valid type of assignement. Instead use arr.set(l, arr.get(i))

    void reverseArrayHelper(Integer l,Integer r,ArrayList<Integer>arr)
    {
        if(l>=r) return;
        int tmp=arr.get(l);
        arr.set(l, arr.get(r));
        arr.set(r, tmp);
        reverseArrayHelper(l+1,r-1,arr);
    }

    void reverseArray(ArrayList<Integer> arr, int m)
    {
        reverseArrayHelper(m+1,arr.size()-1,arr);
    }

[sskadam45]

Episod 6: Correct Solution: Reverse Array:

private static void reverseArrHelper(int l, int r, ArrayList arr){
//base condition 3
if(l >= r)
return;
//do the small task 1
int temp = arr.get(l);
arr.set(l,arr.get(r));
arr.set(r,temp);
//let the recusrsive handle remaining things 2
reverseArrHelper(l+1,r-1,arr);
}
public static void reverseArray(ArrayList arr, int m)
{
reverseArrHelper(m+1, arr.size()-1, arr);
}

[Bhuvaneswari-sura]

in the process of swapping why cant we use the following code
int temp1=arr.get(l);
int temp2=arr.get(r);
arr.add(l,temp2);
arr.add(r,temp1);

[Bhuvaneswari-sura]

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

public class Solution
{ static void reverseArrayhelper(ArrayList arr,int l,int r){
if(l>=r) return;
int temp1=arr.get(l);
int temp2=arr.get(r);
arr.set(l,temp2);
arr.set(r,temp1);
reverseArrayhelper(arr,l+1,r-1);

}
public static void reverseArray(ArrayList arr, int m)
{
// Write your code here.
int n=arr.size()-1;
reverseArrayhelper(arr, m+1,n);
for(int i=0;i<n;i++){
System.out.print(arr.get(i)+" ");
}
}
}
what is wrong with this code