Array of array products - 30 minutes mock interview -

ArrayOfArrayProducts_30mockInterview.cs

using System;

class Solution
{
    public static int[] ArrayOfArrayProducts(int[] arr)  // [1, 2, 3, 4, 5]
    {
      if(arr == null || arr.Length <= 1) // false *
      {
         return new int[0]; 
      }
      
      var length = arr.Length; // 5
      var product = new int[length]; 
      
      int leftToRight = 1; // 1, 1, 2, 2* 3, 2* 3 * 4
      for(int i = 0 ; i < length; i++) // 0 , 1, 2, 3, 4
      {
        product[i] = leftToRight; // 1, 1, 1,
        leftToRight *=  arr[i]; // 1, 1 
      }
      
      int rightToLeft = 1; 
      for(int i = length - 1; i >= 0; i --)
      {
        product[i] *= rightToLeft; 
        rightToLeft *= arr[i]; 
      }
      
      return product; 
    }

    static void Main(string[] args)
    {
      var product = ArrayOfArrayProducts(new int[]{8, 10, 2 }); 
      foreach(var number in product)
      {
        Console.WriteLine(number); 
      }
    }
}

/*

[8, 10, 2]

10 * 2, 8 * 2, 8 * 10 

array with 100 elements 

[1, 2, 3, 4, 5, 6, 7, 8 ,9, 10]

product[8] = 1 * 2 * 3 * 4 * 5 * 6 * 7 * 8 -> 
product[7] = 1 * 2 * 3 * 4 * 5 * 6 * 7 

build dynamic programming 
LeftToRight[0] = 1
LeftToRight[i] = LeftToRight[i - 1] * arr[i - 1];  i > 0 -> save the space -> 
count of multiplication is O(n), otherwise O(n^2)


RightToLeft[len - i]

time complexity : O(n)  multiplication 

O(n)
*/