input: Write a function to find the number of unique paths from a given source to a destination in a grid with dimensions m x n using dynamic programming. Assume that you can only move down or right at any point in time. If the grid is 1x1, return 1.
  def num_unique_paths(m, n):
      dp = [[0 for x in range(m)] for y in range(n)]
    
      for i in range(n):
          dp[i][0] = 1
    
      for j in range(m):
          dp[0][j] = 1
    
      for i in range(1, n):
          for j in range(1, m):
              dp[i][j] = dp[i-1][j] + dp[i][j-1]
    
      return dp[n-1][m-1]
  
  assert num_unique_paths(3, 2) == 3
  assert num_unique_paths(7, 3) == 28
  assert num_unique_paths(1, 1) == 1
  assert num_unique_paths(2, 2) == 2
  assert num_unique_paths(3, 3) == 6
output: def num_unique_paths(m, n):
      dp = [[0 for x in range(m)] for y in range(n)]
    
      for i in range(n):
          dp[i][0] = 1
    
      for j in range(m):
          dp[0][j] = 1
    
      for i in range(1, n):
          for j in range(1, m):
              dp[i][j] = dp[i-1][j] + dp[i][j-1]
    
      return dp[n-1][m-1]