Catalan number - January 20 10:00 PM mock interview - peer asked me how to make an array copy - check reference copy, it does not work. And then use it array.Copy

CatalanNumber_Jan20.cs

using System;

class Solution
{
    public static int NumOfPathsToDest(int n)
    {
      if( n == 0)
      {
        return 0; 
      }
      
      var currentRow  = new int[n]; 
      var previousRow = new int[n]; 
      
      for(int row = 0; row < n; row++) // row = 1
      {
        var firstRow = row == 0; 
        for(int col = 0; col < n; col++)
        {
          if(firstRow)
          {
            currentRow[col] = 1; 
          }
          else 
          {
            currentRow[col] = 0; 
            
            if(row <= col)   // underneath diagnal line 
            {
              currentRow[col] = currentRow[col - 1] + previousRow[col];
            }
          }
        }
        
        // set previous = current
        /*
        for(int col = 0; col < n; col++)
        {
          previousRow[col] = currentRow[col]; 
        }
        */
        Array.Copy(currentRow, previousRow, n); 
      }
      
      return currentRow[n - 1]; 
    }

    static void Main(string[] args)
    {
    }
}
/*
Constaints: 

 (0,0) only can go east(right) or go up (north), you cannnot cross the diagnol line 
 start from (0,0)
 Try to solve path(n-1, n-1) 
 
 x  x  x  x  14 Dest(5 -1 , 5 -1)
 x  x  x  5  14 
 x  x  2  5  9 
 x  1  2  3  4 
 1  1  1  1  1 
 ________________
 0  1  2  3
 
 (0,0)

A[row,j] = 1; row = 0
A[row, col] = A[row, col -1] + A[row - 1, col]      row > 0, row < col 

time complexity O(n * n)
n * n -> keep two rows -> current row / previous row -> space O(n)
*/