Sort 0s and 1s in an Array without Extra Space using Chash

Take two-pointers, low, high. We will use low pointers at the start, and the high pointer will point at the end of the given array.

If array [low] =0, then no swapping required

If array [low] = 1, then swapping is required. Decrement high pointer once.

Time complexity − O(N)

Example

 Live Demo

using System;
namespace ConsoleApplication{
   public class Arrays{
      public void SwapZerosOnes(int[] arr){
         int low = 0;
         int high = arr.Length - 1;
         while (low < high){
            if (arr[low] == 1){
               Swap(arr, low, high);
               high--;
            }
            else{
               low++;
            }
         }
      }
      private void Swap(int[] arr, int pos1, int pos2){
         int temp = arr[pos1];
         arr[pos1] = arr[pos2];
         arr[pos2] = temp;
      }
   }
   class Program{
      static void Main(string[] args){
         Arrays a = new Arrays();
         int[] arr1 = { 0, 1, 1, 0, 1, 1 };
         a.SwapZerosOnes(arr1);
         for (int i = 0; i < arr1.Length; i++){
            Console.WriteLine(arr1[i]);
         }
      }
   }
}

Output

0 0 1 1 1 1