DutchFlag.java

//Java Program to Solve the Dutch National Flag Problem
 
import java.io.BufferedReader;
import java.io.InputStreamReader;
 
public class DutchNationalFlag {
    // Function to solve the Dutch National Flag problem
    static void dutchNationalFlag(int[] array){
        int low,high,middle,temp;
        low = middle = 0;
        high = array.length-1;
        while(middle<=high){
                if(array[middle] == 0)
                {
                    temp = array[low];
                    array[low] = array[middle];
                    array[mid] = temp;
                    low = low + 1;
                    middle  = middle + 1;
                }
                else if(array[middle] == 1)
                    middle++;
                else
                {
                    temp = array[high];
                    array[high] = array[middle];
                    array[middle] = temp;
                    high = high - 1;
                }
        }
    }
 
    // Function to read input and display the output
    public static void main(String[] args) {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int size;
        System.out.println("Enter the size of the array");
        try {
            size = Integer.parseInt(br.readLine());
        } catch (Exception e) {
            System.out.println("Invalid Input");
            return;
        }
        int[] array = new int[size];
        System.out.println("Enter array elements");
        int i;
        for (i = 0; i < array.length; i++) {
            try {
                array[i] = Integer.parseInt(br.readLine());
            } catch (Exception e) {
                System.out.println("An error occurred");
                return;
            }
        }
        System.out.println("The initial array is");
        for(i = 0;i < array.length; i++){
            System.out.print(array[i] + " ");
        }
        dutchNationalFlag(array);
        System.out.println("\nThe final array is");
        for(i = 0;i < array.length; i++){
            System.out.print(array[i] + " ");
        }
    }
}