Reverse String : Recursion

Question

We have to reverse char[] using recursion.

• Input: ["H","a","n","n","a","h"]
• Output: ["h","a","n","n","a","H"]

package codeMonk;

public class RevereseString {

    public  char[] reverseStr(char[] reversedString, int startIndex , int lastIndex, int midIndex) {

        // Base Condition
        if(startIndex > midIndex || midIndex >= lastIndex){
            return reversedString;
        } else {
            char storeChar = reversedString[startIndex];
            reversedString[startIndex] = reversedString[lastIndex -1];
            reversedString[lastIndex -1 ] = storeChar;
            return reverseStr(reversedString, ++startIndex , --lastIndex, midIndex);
        }
    }

    public static void main(String[] args) {
        char[] oldArray = {'A',' ','m','a','n',',',' ','a',' ','p','l','a','n',',',' ','a',' ','c','a','n','a','l',':',' ','P','a','n','a','m','a'};
        int midIndex = 0 + (oldArray.length - 0)/2 ;
        RevereseString reverseStr = new RevereseString();
        char [] newArray = reverseStr.reverseStr(oldArray, 0 , oldArray.length, midIndex);
        for(char ch : newArray) {
            System.out.print(ch +" ");
        }
    }

}

This code works fine, but how can I improve it and reduce the lines of code?

Answer 1

You are not using any stored data in the RevereseString [sic] object, so you do not actually need to create the object. Changing reverseStr() to a static method, (optionally private as well) and you can remove RevereseString reverseStr = new RevereseString(); to save one line of code.

There is no need for a midIndex. You just need to reverse characters until the startIndex and lastIndex meet or cross. Thus you can remove int midIndex = 0 + (oldArray.length - 0)/2 ; and save another line of code.

Finally, you are not returning a new array; you are returning the original oldArray and assigning that object to newArray. In other words, as main() finishes, oldArray == newArray is true. You have reversed the oldArray in place; there is no need for a return value from reverseStr(), so you can eliminate at least another two lines of code.