DutchFlag.java

import java.util.*;
public class DutchFlag {
    private static void dutchNationalFlag(int[] array, int size){
        int start = 0 , mid = 0;
        int end = size-1;

        while(mid < end){
            switch(array[mid]){
                case 0:
                    swap(array,start,mid);
                    start++;
                    mid++;
                    break;
                case 1:
                    mid++;
                    break;
                case 2:
                    swap(array,mid,end);
                    end--;
                    break;
            }
        }
    }
    private static void swap(int[] array, int i, int j){
        int temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int size = sc.nextInt();
        int[] array = new int[size];
        //Input Array:

        for(int i = 0; i < size; i++){
            array[i] = sc.nextInt();
        }

        dutchNationalFlag(array,size);
        //Output
        System.out.println("Sorted Array : ");

        for(int i = 0; i < size; i++){
            System.out.print(array[i]+" ");
        }
    }
}
//Sample output : 
// 8 ->size
// 0 1 2 2 1 1 0 0 -> input array
//Output : s
// Sorted Array : 
// 0 0 0 1 1 1 2 2