Catalan number practice - C# code

CatalanNumber_practice.cs

using System;

class Solution
{
    public static int NumOfPathsToDest(int n)
    {
      // your code goes here
      if( n < 0)
      {
        return -1; 
      }
      
      if( n == 0)
      {
        return 1; 
      }
      
      var paths = new int[n, n];           
      
      for(int row = 0; row < n; row ++)
      {
        var isFirstRow = row == 0;         
        
        for(int col = 0; col < n; col ++)
        {
          if(isFirstRow)
          {
            paths[0, col] = 1; // only by going right
          }
          else if( row > col)
          {
            paths[row, col] = 0; 
          }
          else if( row == col)
          {
            paths[row, col] = paths[row - 1, col]; 
          }
          else if ( row < col)  // (4,5) -> (3, 5) go north, (4, 4) -> right
          {
            paths[row, col] = paths[row - 1, col] + paths[row, col - 1]; 
          }          
        }               
      }
      
      return paths[n -1, n - 1]; 
    }

    static void Main(string[] args)
    {

    }
}

// n = 4, output = 5 
//NOT accepted (i >= j: xVal >= yVal)
// (1,0) -> (0,0) -> right NPD(1,0) = NPD(0,0)
// NPD(n, 0) = NPD(0,0) = 1, n from 0 to 5
// NPD(row, col), col > row , NPD(rol, col) = 0
// NPD(row, row) = NPD( row, row -1 ), row >= 1, on the red line 
// NPD(row, col), if col < row, then NPD(row, col) = NPD(row -1, col) + NPD(row, col -1)
//
// int[n,n]                                                   -> right
// base case -> row = 0