using System;

using System.Linq;

public class Program

{

    public static int[] SortColors(int[] nums) {

        int n = nums.Length, red = 0, white = 0, blue = 0;

        for(int i = 0; i < n; i++){

            if(nums[i] == 0){

                red++;

            }

            else if(nums[i] == 1){

                white++;

            }

            else if(nums[i] == 2){

                blue++;

            }

        }

        for(int j = 0; j < n; j++){

            if(j < red){

                nums[j] = 0;

            }

            else if(j >= red && j < white + red){

                nums[j] = 1;

            }

            else {

                nums[j] = 2;

            }

        }

        return nums;

    }

    public static void SortColorTester(){

        // Two loops, O(2n) ——> O(n)

        Console.WriteLine(SortColors(new int[] {2,0,2,1,1,0}).SequenceEqual(new int[] {0,0,1,1,2,2}) ? "PASS" : "FAIL");

        Console.WriteLine(SortColors(new int[] {1}).SequenceEqual(new int[] {1}) ? "PASS" : "FAIL");

        Console.WriteLine(SortColors(new int[] {2,2,2,0,0,0,1,1,1}).SequenceEqual(new int[] {0,0,0,1,1,1,2,2,2}) ? "PASS" : "FAIL");

        Console.WriteLine(SortColors(new int[] {0,1,2,1,0,2,2,1,2}).SequenceEqual(new int[] {0,0,1,1,1,2,2,2,2}) ? "PASS\n" : "FAIL\n");

    }

    public static void Main()

    {

        SortColorTester();

    }

}