4

How to print the reverse of the String java is object orientated language without using any predefined function like reverse()?

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4
  • 12
    I also think "any predefine function" is very vague... if you don't use any predefined functions, you're going to struggle to do anything. Commented Apr 10, 2010 at 10:23
  • 8
    Furtunately Java only has Methods, it doesn't have functions. ;) Commented Jul 24, 2010 at 13:23
  • possible duplicate of Whats the best way to recursively reverse a string in Java? Commented Sep 27, 2011 at 15:15
  • refer learnjava-soa.blogspot.in/2016/02/… Commented Feb 15, 2016 at 7:18

34 Answers 34

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1
2
58

This is the simplest solution:

System.out.print("egaugnal detatneiro tcejbo si avaj");
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2 Comments

This is what happens when people don't ask questions properly.
I think StackOverflow should implement smileys :)
50

You can do it either recursively or iteratively (looping).

Iteratively:

 static String reverseMe(String s) {
   StringBuilder sb = new StringBuilder();
   for(int i = s.length() - 1; i >= 0; --i)
     sb.append(s.charAt(i));
   return sb.toString();
 }

Recursively:

 static String reverseMe(String s) {
   if(s.length() == 0)
     return "";
   return s.charAt(s.length() - 1) + reverseMe(s.substring(0,s.length()-1));
 }
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6 Comments

-1 for just posting a copy and paste solution for such an obvious homework assignment.
To downvoters: please read the guidelines: meta.stackexchange.com/questions/10811/… : "Don't downvote others who answer homework questions in good faith, even if they break these guidelines."
@polygenelubricants looks like most agree that this is an obvious homework question and the guidelines talk about non obvious ones.
for homework questions, it may be a good practice to include a bit of explanation so that it does not turn into Ctrl-C, Ctrl-V
charAt() and length() are String functions.
|
8

Well, printing itself would suggest a predefined function...

Presumably, though, you could obtain the characters and concatenate them manually in reverse (i.e. loop over it backwards). Of course, you could say concatenation is a predefined function... so maybe the char array itself. But again... why?

Is the source allowed to contain "egaugnal detatneiro tcejbo si avaj" ;-p

Also - note that string reversal is actually pretty complex if you consider unicode combining characters, surrogate pairs, etc. You should note the caveat that most string reversal mechanisms will only deal with the more common cases, but may struggle with i18n.

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Comments

7 
String reverse(String s) {
  int legnth = s.length();
  char[] arrayCh = s.toCharArray();
  for(int i=0; i< length/2; i++) {
      char ch = s.charAt(i);
      arrayCh[i] = arrayCh[legnth-1-i];
      arrayCh[legnth-1-i] = ch;
  } 
 return new String(arrayCh);
}
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6

How about a simple traverse from the end of the string to the beg:

void printRev(String str) {
 for(int i=str.length()-1;i>=0;i--)
  System.out.print(str.charAt(i));
}
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3 
public class StringReverse {

    public static void main(String[] args) {
        String s= (args[0]);
        for (int i =s.length()-1; i >= 0; i--) {            
               System.out.print(s.charAt(i));    
        }
    } 
}

Prints the reversed string of the input.

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Comments

3 
String a="Siva";

for(int i=0;i<=a.length()-1;i++){
    System.out.print(a.charAt(i));
}

for(int i = a.length() - 1; i >= 0; --i){
    System.out.println(a.charAt(i)); 
}
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Comments

3

First of all: Why reinvent the wheel?

That being said: Loop from the length of the string to 0 and concatenate into another string.

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1

Here's a recursive solution that just prints the string in reverse order. It should be educational if you're trying to learn recursion. I've also made it "wrong" by actually having 2 print statements; one of them should be commented out. Try to figure out which mentally, or just run experiments. Either way, learn from it.

static void printReverse(String s) {
    if (!s.isEmpty()) {
        System.out.print(s.substring(0, 1));
        printReverse(s.substring(1));
        System.out.print(s.substring(0, 1));
    }
}

Bonus points if you answer these questions:

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Comments

1 
final String s = "123456789";
final char[] word = s.toCharArray();
final int l = s.length() - 2;
final int ll = s.length() - 1;
for (int i = 0; i < l; i++) {
    char x = word[i];
    word[i] = word[ll - i];
    word[ll - i] = x;
}
System.out.println(s);
System.out.println(new String(word));

You can do it either recursively or iteratively (looping).

Iteratively:

static String reverseMe(String s) {
    StringBuilder sb = new StringBuilder();
    for (int i = s.length() - 1; i >= 0; --i)
        sb.append(s.charAt(i));
    return sb.toString();
}

Recursively:

static String reverseMe(String s) {
    if (s.length() == 0)
        return "";
    return s.charAt(s.length() - 1) + reverseMe(s.substring(1));
}

Integer i = new Integer(15);
test(i);
System.out.println(i);
test(i);
System.out.println(i); 
public static void test (Integer i) {
    i = (Integer)i + 10;
}
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1 Comment

return s.charAt(s.length() - 1) + reverseMe(s.substring(1)); is wrong instead it should be return s.charAt(s.length() - 1) + reverseMe(s.substring(0,s.length()));
1 
public class StringReverse {
    public static void main(String ar[]){
        System.out.println(reverseMe("SRINIVAS"));
    }
    static String reverseMe(String s){
        StringBuffer sb=new StringBuffer();
        for(int i=s.length()-1;i>=0;--i){
            sb.append(s.charAt(i));
        }
        return sb.toString();
    }
}
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Comments

1 
private void rev() {
    String st="hello";
    String b="";

    for(int i=st.length()-1;i>=0;i--){
        b=b+st.charAt(i);
    }

    System.out.println("reverse:::"+b);
}
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Comments

1

Try this:

public  class Test {

    public static void main(String[] args) {
        String s = "welcome";   
    for( int i=0, j = (s.length())-1; i <= j; j-- ) {   
      char c=s.charAt(j);
      System.out.print(c);
    }
    }
}
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1

What is suprising is that most of the answers are wrong! When Unicode is used. Seems like no one understands that java uses UTF-16 under the hood for Text encoding.

Here is my simple answer.

static String reverseMe(String s) {
   StringBuilder sb = new StringBuilder();

   int count = s.codePointCount(0,s.length());
   for(int i = count - 1; i >= 0; --i)
     sb.append(Character.toChars(s.codePointAt(i)));

   return sb.toString();
 }
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2 Comments

Similar solution using java.text.BreakIterator: stackoverflow.com/a/20279110/9636
Thanks Heath Borders. I didn't really go in Precomposed character (I don't think most people know what they're). In the above it no doubt will break reversing a string that used them.
1

this is the best solution for this

public class String_rev {
public static void main(String[] args) {
    String str="Karan Rajput";
    int ln=str.length();
    for (int i = ln; i > 0; i--) {
        System.out.print(str.charAt(i-1));
    }
}

}

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1 Comment

So many methods were already provided that does this method. I don't see how this can benefit when it is simply a derivative of the other posts.
0 
public class ReverseString {

public static void main(String [] args) {

    String s = "reverse string" ;
    String b = "";

            for (int i = 0; i < s.length(); i++ ){
                 b= b + s.substring(s.length()-1-i, s.length()-i);

                 }

             System.out.println(b);
}
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2 Comments

easiest way to do it without using any specific method.
Welcome to stackoverflow. That is very similar to previous suggestions. Given the age of this thread, it is best not to resurrect it unless the response contributes something significantly different than previous answers.
0 
public static void main(String[] args) {


    String str = "hello world here I am";

    StringTokenizer strToken = new StringTokenizer(str);
    int token = strToken.countTokens();
    String str1 [] = new String[token];

    char chr[] = new char[str.length()];
    int counter = 0;

    for(int j=0; j < str.length(); j++) {

        if(str.charAt(j) != ' ') {
            chr[j] = str.charAt(j);
        }else {
            str1[counter++] = new String(chr).trim();
            chr = new char[str.length()];
        }
    }
    str1[counter++] = new String(chr).trim();

    for(int i=str1.length-1; i >= 0 ; i--) {
        System.out.println(str1[i]);
    }
}

O/P is: am I here world hello

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0

I had this a while back, and having answered with the obvious StringBuffer.reverse() answer, they then asked 'Can you reverse a char array without using those API methods and achieve the result without spooling into a new char array?'

At the time I recognised that I only needed to iterate over half the length of the char array, but made a bit of a hash of explaining the actual code that needed to go into it (it was a verbal question). Anyway, I tried it when I got home and came up with this:

public class StringReverse {

public static void main(String[] args){

    String a = "String";

    char[] aChar = a.toCharArray();

    for (int i = (aChar.length-1)/2 ; i >= 0 ; i--){
        int posA = i;
        int posB = (aChar.length-1-i);
        char tmpA = aChar[posA];
        char tmpB = aChar[posB];
        System.out.println("Setting " + posA + " to " + tmpB);
        System.out.println("Setting " + posB + " to " + tmpA);

        aChar[posA] = tmpB;
        aChar[posB] = tmpA;
    }

    System.out.println(aChar);
}

}

You can obviously achieve this with less code, but I think the temporary assignments in the method make it more clear what the code is doing.

Outputs something like:

Setting 2 to i
Setting 3 to r
Setting 1 to n
Setting 4 to t
Setting 0 to g
Setting 5 to S

gnirtS

More of an interview question than a homework question, I'd say.

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0 
public String reverse(String arg)
{
    String tmp = null;
    if (arg.length() == 1)
    {
        return arg;
    }

    else
    {

        String lastChar = arg.substring(arg.length()-1,arg.length());

        String remainingString = arg.substring(0, arg.length() -1);

        tmp = lastChar + reverse(remainingString);
        return tmp;


    }
}
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0 
import java.util.*;
public class Restring {

public static void main(String[] args) {
  String input,output;
  Scanner kbd=new Scanner(System.in);
  System.out.println("Please Enter a String");
  input=kbd.nextLine();
  int n=input.length();

  char tmp[]=new char[n];
  char nxt[]=new char[n];

  tmp=input.toCharArray();
  int m=0;
  for(int i=n-1;i>=0;i--)
  {
      nxt[m]=tmp[i];
      m++;
  }

  System.out.print("Reversed String is   ");
  for(int i=0;i<n;i++)
  {
      System.out.print(nxt[i]);
  }

}
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0 
 public class ReverseWithoutStringAPI {

public static void main(String[] args) {

      String st="hello";

        StringBuffer b=new StringBuffer();

        for(int i=st.length()-1;i>=0;i--){

            b.append(st.charAt(i)); }

        System.out.println("reverse:::"+b);
}
}
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0 
String x = "stack overflow";
String reversed = "";
for(int i = x.length()-1 ; i>=0; i--){
    reversed = reversed+ x.charAt(i);
}
System.out.println("reversed string is : "+ reversed);
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0

Here you go: 




public static void main (String[] args) {
    System.out.println(reverserString("Akshay"));
}

private static String reverserString(String src) {
    char[] sArr = src.toCharArray();
    char[] dArr = new char[sArr.length];
    for(int i=sArr.length; i>0; i--) {
        dArr[sArr.length-i] = sArr[i-1];
    }

    return new String(dArr);
}

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0 
public class MyStack {
   private int maxSize;
   private char[] stackArray;
   private int top;
   public MyStack(int s) {
      maxSize = s;
      stackArray = new char[maxSize];
      top = -1;
   }
   public void push(char j) {
      stackArray[++top] = j;
   }
   public char pop() {
      return stackArray[top--];
   }
   public char peek() {
      return stackArray[top];
   }
   public boolean isEmpty() {
      return (top == -1);
   }
   public boolean isFull() {
      return (top == maxSize - 1);
   }
   public static void main(String[] args) {
      MyStack theStack = new MyStack(10);
      String s="abcd";
      for(int i=0;i<s.length();i++)
      theStack.push(s.charAt(i));
      for(int i=0;i<s.length();i++)
      System.out.println(theStack.pop());

    }
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0 
public class ReverseString {

public static void main(String[] args) {

    reverseString("HELLO");
}

public static String reverseString(String s){
    char []arr=s.toCharArray();
    for(int i= (arr.length)-1;i>=0;i--){
        System.out.print(arr[i]);
    }
    String str=String.copyValueOf(arr);
    return str;
}
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Comments

0 
package com.ofs;

public class ReverseWordsInString{
public static void main(String[] args) {

    String str = "welcome to the new world and how are you feeling ?";

    // Get the Java runtime
    Runtime runtime = Runtime.getRuntime();
    // Run the garbage collector
    runtime.gc();
    // Calculate the used memory
    long firstUsageMemory = runtime.totalMemory() - runtime.freeMemory();
    System.out.println("Used memory in bytes: " + firstUsageMemory);
    System.out.println(str);
    str = new StringBuffer(str).reverse().toString();
    int count = 0;
    int preValue = 0;
    int lastspaceIndexVal = str.lastIndexOf(" ");
    int strLen = str.length();
    for (int i = 0; i < strLen - 1; i++) {
        if (Character.isWhitespace(str.charAt(i))) {
            if (i - preValue == 1 && count == 0) {
                str = str.substring(0, preValue) + str.charAt(i - 1)
                        + str.substring(i, strLen);
                preValue = i;
                count++;
            } else if (i - preValue == 2 && count == 0) {
                str = str.substring(0, preValue) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.substring(i, strLen);
                preValue = i;
                count++;
            } else if (i - preValue == 3 && count == 0) {
                str = str.substring(0, preValue) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.charAt(i - 3)
                        + str.substring(i, strLen);
                preValue = i;
                count++;
            } else if (i - preValue == 4 && count == 0) {
                str = str.substring(0, preValue) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.charAt(i - 3)
                        + str.charAt(i - 4) + str.substring(i, strLen);
                preValue = i;
                count++;
            } else if (i - preValue == 5 && count == 0) {
                str = str.substring(0, preValue) + str.charAt(i - 1)
                        + str.substring(i - 2, i - 1) + str.charAt(i - 3)
                        + str.charAt(i - 3) + str.charAt(i - 5)
                        + str.substring(i, strLen);
                preValue = i;
                count++;
            } else if (i - preValue == 6 && count == 0) {
                str = str.substring(0, preValue) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.charAt(i - 3)
                        + str.charAt(i - 4) + str.charAt(i - 5)
                        + str.charAt(i - 6) + str.substring(i, strLen);
                preValue = i;
                count++;
            } else if (i - preValue == 7 && count == 0) {
                str = str.substring(0, preValue) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.charAt(i - 3)
                        + str.charAt(i - 4) + str.charAt(i - 5)
                        + str.charAt(i - 6) + str.charAt(i - 7)
                        + str.substring(i, strLen);
                preValue = i;
                count++;
            } else if (i - preValue == 8 && count == 0) {
                str = str.substring(0, preValue) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.charAt(i - 3)
                        + str.charAt(i - 4) + str.charAt(i - 5)
                        + str.charAt(i - 6) + str.charAt(i - 7)
                        + str.charAt(i - 8) + str.substring(i, strLen);
                preValue = i;
                count++;
            } else if (i - preValue == 2 && count != 0) {
                str = str.substring(0, preValue) + str.charAt(i - 1)
                        + str.substring(i, strLen);
                preValue = i;
            } else if (i - preValue == 3 && count != 0) {
                str = str.substring(0, preValue + 1) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.substring(i, strLen);
                preValue = i;
            } else if (i - preValue == 4 && count != 0) {
                str = str.substring(0, preValue + 1) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.charAt(i - 3)
                        + str.substring(i, strLen);
                preValue = i;
            } else if (i - preValue == 5 && count != 0) {
                str = str.substring(0, preValue + 1) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.charAt(i - 3)
                        + str.charAt(i - 4) + str.substring(i, strLen);
                preValue = i;
                count++;
            } else if (i - preValue == 6 && count != 0) {
                str = str.substring(0, preValue + 1) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.charAt(i - 3)
                        + str.charAt(i - 4) + str.charAt(i - 5)
                        + str.substring(i, strLen);
                preValue = i;
                count++;
            } else if (i - preValue == 7 && count != 0) {
                str = str.substring(0, preValue + 1) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.charAt(i - 3)
                        + str.charAt(i - 4) + str.charAt(i - 5)
                        + str.charAt(i - 6) + str.substring(i, strLen);
                preValue = i;
                count++;
            } else if (i - preValue == 8 && count != 0) {
                str = str.substring(0, preValue + 1) + str.charAt(i - 1)
                        + str.charAt(i - 2) + str.charAt(i - 3)
                        + str.charAt(i - 4) + str.charAt(i - 5)
                        + str.charAt(i - 6) + str.charAt(i - 7)
                        + str.substring(i, strLen);
                preValue = i;
                count++;
            }
            if (lastspaceIndexVal == preValue) {
                if (strLen - lastspaceIndexVal == 2 && count != 0) {
                    str = str.substring(0, preValue + 1)
                            + str.charAt(strLen - 1);
                    preValue = i;
                } else if (strLen - lastspaceIndexVal == 3 && count != 0) {
                    str = str.substring(0, preValue + 1)
                            + str.charAt(strLen - 1)
                            + str.charAt(strLen - 2);
                    preValue = i;
                } else if (strLen - lastspaceIndexVal == 4 && count != 0) {
                    str = str.substring(0, preValue + 1)
                            + str.charAt(strLen - 1)
                            + str.charAt(strLen - 2)
                            + str.charAt(strLen - 3);
                    preValue = i;
                    count++;
                } else if (strLen - lastspaceIndexVal == 5 && count != 0) {
                    str = str.substring(0, preValue + 1)
                            + str.charAt(strLen - 1)
                            + str.charAt(strLen - 2)
                            + str.charAt(strLen - 3)
                            + str.charAt(strLen - 4);
                    preValue = i;
                } else if (strLen - lastspaceIndexVal == 6 && count != 0) {
                    str = str.substring(0, preValue + 1)
                            + str.charAt(strLen - 1)
                            + str.charAt(strLen - 2)
                            + str.charAt(strLen - 3)
                            + str.charAt(strLen - 4)
                            + str.charAt(strLen - 5);
                    preValue = i;
                    count++;
                } else if (strLen - lastspaceIndexVal == 7 && count != 0) {
                    str = str.substring(0, preValue + 1)
                            + str.charAt(strLen - 1)
                            + str.charAt(strLen - 2)
                            + str.charAt(strLen - 3)
                            + str.charAt(strLen - 4)
                            + str.charAt(strLen - 5)
                            + str.charAt(strLen - 6);
                    preValue = i;
                } else if (strLen - lastspaceIndexVal == 8 && count != 0) {
                    str = str.substring(0, preValue + 1)
                            + str.charAt(strLen - 1)
                            + str.charAt(strLen - 2)
                            + str.charAt(strLen - 3)
                            + str.charAt(strLen - 4)
                            + str.charAt(strLen - 5)
                            + str.charAt(strLen - 6)
                            + str.charAt(strLen - 7);
                    preValue = i;
                }
            }
        }
    }
    runtime.gc();
    // Calculate the used memory
    long SecondaryUsageMemory = runtime.totalMemory()
            - runtime.freeMemory();
    System.out.println("Used memory in bytes: " + SecondaryUsageMemory);
    System.out.println(str);
}
}
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0

ReverseString.java

public class ReverseString {
    public static void main(String[] args) {
        String str = "Ranga Reddy";
        String revStr = reverseStr(str);
        System.out.println(revStr);     
    }

    // Way1 - Recursive
    public static String reverseStr(String str) {
        char arrStr[] = reverseString(0, str.toCharArray());
        return new String(arrStr);
    }

    private static char[] reverseString(int charIndex, char[] arr) {     
        if (charIndex > arr.length - (charIndex+1)) {
          return arr;
        }

        int startIndex = charIndex;
        int endIndex = arr.length - (charIndex+1);

        char temp = arr[startIndex];        
        arr[startIndex] = arr[endIndex];
        arr[endIndex] = temp;      
        charIndex++;       
        return reverseString(charIndex++, arr);
    }

    // Way2
    private static String strReverse(String str) {
        char ch[] = new char[str.length()];
        for (int i = str.length() - 1, j = 0; i >= 0; i--) {
            ch[j++] = str.charAt(i);
        }
        return new String(ch);
    }
}
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0

It is very simple using while loop

public class Test {
public static void main(String[] args) {
    String name = "subha chandra";
    int len = name.length();
    while(len > 0){
        len--;
        char c = name.charAt(len);
        System.out.print(c); // use String.valueOf(c) to convert char to String
    }
}    
}
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0 
import java.util.Scanner;
public class StringReverse {
    public static void main(String[] args) {
        //Read user Data From Console
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter Your String:");
        //Take an String so that it can Store the string data 
        String s1 = sc.nextLine();
        //split the string and keep in an array
        String[] s2 = s1.split(" ");
        String s3 = " ";
        //reverse  the string and placed in an String s3
        for (int i = 0; i < s2.length; i++) {
            for (int j= s2[i].length()-1;j>=0;j--) {
                s3 += s2[i].charAt(j);
            }//for
            s3 += " ";
        }//for

        System.out.println("After Reverse: "+s3);

    }//main
}//StringReverse
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Comments

0

It can be done this way also 

char c[]=str.toCharArray();
  int i=c.lenght-1;
public void printReverseString(char[] c, int i){
       if(i==-1) return;
       System.out.println(c[i]);
       printReverseString(c,--i);
   }
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2

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