input: 
  def num_unique_paths(m: int, n: int) -> int:
      """
      Find the number of unique paths from a given source to a destination in a m x n grid.
      Only moves right or down are allowed.
      
      >>> num_unique_paths(2, 3)
      3
      >>> num_unique_paths(3, 3)
      6
      >>> num_unique_paths(7, 3)
      28
      """
      dp = [[0 for x in range(m)] for y in range(n)] 
    
      # Count of paths to reach any
      # cell in first column is 1  
      for i in range(n): 
          dp[i][0] = 1
    
      # Count of paths to reach any
      # cell in first column is 1  
      for j in range(m): 
          dp[0][j] = 1
    
      # Calculate count of paths for other 
      # cells in bottom-up manner using
      # the recursive solution 
      for i in range(1, n): 
          for j in range(1, m): 
    
              # By uncommenting the last
              # part the code calculatest he total
              # possible paths if the diagonal 
              # Movements are allowed 
              dp[i][j] = dp[i-1][j] + dp[i][j-1]# + dp[i-1][j-1]
    
      return dp[n-1][m-1]
  
output:     dp = [[0 for x in range(n)] for y in range(m)] 
    
      # Count of paths to reach any
      # cell in first row is 1  
      for i in range(m): 
          dp[i][0] = 1
    
      # Count of paths to reach any
      # cell in first column is 1  
      for j in range(n): 
          dp[0][j] = 1
    
      # Calculate count of paths for other 
      # cells in bottom-up manner using
      # the recursive solution 
      for i in range(1, m): 
          for j in range(1, n): 
    
              # By uncommenting the last
              # part the code calculatest he total
              # possible paths if the diagonal 
              # Movements are allowed 
              dp[i][j] = dp[i-1][j] + dp[i][j-1]# + dp[i-1][j-1]
    
      return dp[m-1][n-1]