Segregating ‘R’ ‘G’ ‘B’ in a string in Java

In this Java tutorial, we will learn how to segregate R G B in a string in Java. You will find easy to understand algorithm with an easy code snippet. Input and output are also provided.

Problem: Separate R G B in a string in Java

We are given with a string “s” consists of characters ‘R’, ‘G’ and ‘B’. We have to segregate the characters in such a way that all ‘R’ comes in left of string, all ‘B’ in middle and all ‘G’ in right.

This problem is also a part of the famous Dutch national flag algorithm. In this Java tutorial, we are going to solve this problem by using switch statement.

How to split a string into array of characters in Java?

To split a string into array of characters we use string.CharArray() function in Java.

Syntax:- char[] s = str.toCharArray();

Algorithm:-

Take three variables low , mid , high.
Initialize low=0,mid=0,high=n-1.
pass a[mid] as variable in switch condition.
Whenever ‘R’ comes to swap a[mid] and a[low] and increment low and mid.
Whenever ‘B’ comes just increment mid.
Whenever ‘G’ comes to swap a[mid] and a[high] and decrement high.

Code Snippet to segregate R G B in a string in Java

while(mid<=high)
      {
          switch(s[mid])
          {
              case 'R' :
                          temp = s[low];
                          s[low] = s[mid];
                           s[mid] = temp;
                               low++; mid++;
                              break;
               case 'B' :
                          mid++;
                           break;
                           
               case 'G' :
                            temp = s[mid];
                            s[mid] = s[high];
                             s[high] = temp;
                               high--; 
                               break;
          }
      }

Java code to segregate ‘R’ ‘G’ and ‘B’ in a string

import java.util.Scanner;
import java.util.*;

class Codespeedy
{
    public static void segregate(String str)
    {
        int n=str.length();
       int low=0 , mid=0 , high=n-1;
       
       char[] s = str.toCharArray();
       
         char temp;
       
       while(mid<=high)
       {
           switch(s[mid])
           {
               case 'R' :
                           temp = s[low];
                           s[low] = s[mid];
                            s[mid] = temp;
                                low++; mid++;
                               break;
                            
                case 'B' :
                           mid++;
                            break;
                            
                case 'G' :
                             temp = s[mid];
                             s[mid] = s[high];
                              s[high] = temp;
                                high--; 
                                break;
           }
       }
        System.out.print(s);
    }
    
       public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        
           String str = scan.nextLine();
           
           segregate(str);
    }
}

INPUT

RBRGRGBBRGBGR

OUTPUT

RRRRRBBBBGGGG

This type of problem also comes under the category of famous DutchFlagProblem.

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