dutchFlag.java

import java.util.*;

public class dutchFlag {
    public static void sortArray(ArrayList<Integer> arr, int n) {
        int low = 0, mid = 0, high = n - 1; // 3 pointers

        while (mid <= high) {
            if (arr.get(mid) == 0) {
                // swapping arr[low] and arr[mid]
                int temp = arr.get(low);
                arr.set(low, arr.get(mid));
                arr.set(mid, temp);

                low++;
                mid++;

            } else if (arr.get(mid) == 1) {
                mid++;

            } else {
                // swapping arr[mid] and arr[high]
                int temp = arr.get(mid);
                arr.set(mid, arr.get(high));
                arr.set(high, temp);

                high--;
            }
        }
    }

    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the number of elements in array: ");
        int n= sc.nextInt();
        ArrayList<Integer> arr = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            System.out.print("Enter element " + (i+1)+"->");
            int x = sc.nextInt();
            arr.add(x);

        }
        sortArray(arr, n);
        System.out.println("After sorting:");
        for (int i = 0; i < n; i++) {
            System.out.print(arr.get(i) + " ");
        }
        System.out.println();

    }

}