DutchNationalFlagProb.cpp

//The flag of the Netherlands consists of three colors: white, red, and blue. 
//The task is to randomly arrange balls of white, red, and blue such that balls of the same color are placed together.
//For simplicity we assume the numbers 0,1,2 in the place of the colors white, red and blue. 
//Therefore the array is assumed to have values in {0, 1, 2}  

#include<iostream> 
#include<stdio.h>

using namespace std;  

// Function to sort the input array, 

void DNFS(int arr[], int arr_size)  
{  
    int low = 0;  
    int high = arr_size - 1;  
    int mid = 0;  
      
    // Iterate till all the elements are sorted
    
    while (mid <= high)  
    {  
        switch (arr[mid])  
        {  
              
            // mid is 0  
        case 0:  
            swap(arr[low++], arr[mid++]);  
            break;  
              
            // mid is 1 .  
        case 1:  
            mid++;  
            break;  
              
            // mid is 2  
        case 2:  
            swap(arr[mid], arr[high--]);  
            break;  
        }  
    }  
}  
  
  
  
// Function to print array arr[]  
void printArray(int arr[], int arr_size)  
{  
    // Iterate and print every element  
    for (int i = 0; i < arr_size; i++)  
        cout << arr[i] << " ";  
  
}  
  
// Driver Code  
int main()  
{  
    int arr[] = {0,0,1,2,0,1,2};  
    int n = sizeof(arr)/sizeof(arr[0]);  

    cout << "Array before running the algorithm: ";  
      
    printArray(arr, n);   
    
    DNFS(arr, n);  
  
    cout << "\nArray after DNFS algorithm: ";  
      
    printArray(arr, n);  
  
    return 0;  
}